Element locking 'off' by default (so they dont move when the screenshot scroll happens), only lock top viewport elements. Improve logging.

.github/workflows/containers.yml

@@ -15,7 +15,6 @@ on:
   push:
     branches:
       - master
-      - dev
 
 jobs:
   metadata:
@@ -93,17 +92,28 @@ jobs:
           version: latest
           driver-opts: image=moby/buildkit:master
 
-      # dev branch -> :dev container tag
+      # master branch -> :dev container tag
+      - name: Docker meta :dev
+        if: ${{ github.ref == 'refs/heads/master' && github.event_name != 'release' }}
+        uses: docker/metadata-action@v5
+        id: meta_dev
+        with:
+          images: |
+            ${{ secrets.DOCKER_HUB_USERNAME }}/changedetection.io
+            ghcr.io/${{ github.repository }}
+          tags: |
+            type=raw,value=dev
+
       - name: Build and push :dev
         id: docker_build
-        if: ${{ github.ref == 'refs/heads/dev' }}
+        if: ${{ github.ref == 'refs/heads/master' && github.event_name != 'release' }}
         uses: docker/build-push-action@v6
         with:
           context: ./
           file: ./Dockerfile
           push: true
-          tags: |
-            ${{ secrets.DOCKER_HUB_USERNAME }}/changedetection.io:dev,ghcr.io/${{ github.repository }}:dev
+          tags: ${{ steps.meta_dev.outputs.tags }}
+          labels: ${{ steps.meta_dev.outputs.labels }}
           platforms: linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v8
           cache-from: type=gha
           cache-to: type=gha,mode=max
@@ -142,6 +152,7 @@ jobs:
           file: ./Dockerfile
           push: true
           tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
           platforms: linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v8
           cache-from: type=gha
           cache-to: type=gha,mode=max

Dockerfile

@@ -78,6 +78,12 @@ RUN --mount=type=cache,id=pip,sharing=locked,target=/tmp/pip-cache \
 # Final image stage
 FROM python:${PYTHON_VERSION}-slim-bookworm
 LABEL org.opencontainers.image.source="https://github.com/dgtlmoon/changedetection.io"
+LABEL org.opencontainers.image.url="https://changedetection.io"
+LABEL org.opencontainers.image.documentation="https://changedetection.io/tutorials"
+LABEL org.opencontainers.image.title="changedetection.io"
+LABEL org.opencontainers.image.description="Self-hosted web page change monitoring and notification service"
+LABEL org.opencontainers.image.licenses="Apache-2.0"
+LABEL org.opencontainers.image.vendor="changedetection.io"
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libxslt1.1 \

changedetectionio/content_fetchers/base.py

@@ -71,10 +71,19 @@ class Fetcher():
     supports_screenshots = False        # Can capture page screenshots
     supports_xpath_element_data = False # Can extract xpath element positions/data for visual selector
 
+    # Screenshot element locking - prevents layout shifts during screenshot capture
+    # Only needed for visual comparison (image_ssim_diff processor)
+    # Locks element dimensions in the first viewport to prevent headers/ads from resizing
+    lock_viewport_elements = False      # Default: disabled for performance
+
     def __init__(self, **kwargs):
         if kwargs and 'screenshot_format' in kwargs:
             self.screenshot_format = kwargs.get('screenshot_format')
 
+        # Allow lock_viewport_elements to be set via kwargs
+        if kwargs and 'lock_viewport_elements' in kwargs:
+            self.lock_viewport_elements = kwargs.get('lock_viewport_elements')
+
 
     @classmethod
     def get_status_icon_data(cls):

changedetectionio/content_fetchers/playwright.py

@@ -10,18 +10,21 @@ from changedetectionio.content_fetchers import SCREENSHOT_MAX_HEIGHT_DEFAULT, vi
 from changedetectionio.content_fetchers.base import Fetcher, manage_user_agent
 from changedetectionio.content_fetchers.exceptions import PageUnloadable, Non200ErrorCodeReceived, EmptyReply, ScreenshotUnavailable
 
-async def capture_full_page_async(page, screenshot_format='JPEG'):
+async def capture_full_page_async(page, screenshot_format='JPEG', watch_uuid=None, lock_viewport_elements=False):
     import os
     import time
     import multiprocessing
 
     start = time.time()
+    watch_info = f"[{watch_uuid}] " if watch_uuid else ""
 
+    setup_start = time.time()
     page_height = await page.evaluate("document.documentElement.scrollHeight")
     page_width = await page.evaluate("document.documentElement.scrollWidth")
     original_viewport = page.viewport_size
+    dimensions_time = time.time() - setup_start
 
-    logger.debug(f"Playwright viewport size {page.viewport_size} page height {page_height} page width {page_width}")
+    logger.debug(f"{watch_info}Playwright viewport size {page.viewport_size} page height {page_height} page width {page_width} (got dimensions in {dimensions_time:.2f}s)")
 
     # Use an approach similar to puppeteer: set a larger viewport and take screenshots in chunks
     step_size = SCREENSHOT_SIZE_STITCH_THRESHOLD # Size that won't cause GPU to overflow
@@ -29,25 +32,31 @@ async def capture_full_page_async(page, screenshot_format='JPEG'):
     y = 0
     elements_locked = False
 
-    if page_height > page.viewport_size['height']:
-
-        # Lock all element dimensions BEFORE screenshot to prevent CSS media queries from resizing
-        # capture_full_page_async() changes viewport height which triggers @media (min-height) rules
+    # Only lock viewport elements if explicitly enabled (for image_ssim_diff processor)
+    # This prevents headers/ads from resizing when viewport changes
+    if lock_viewport_elements and page_height > page.viewport_size['height']:
+        lock_start = time.time()
         lock_elements_js_path = os.path.join(os.path.dirname(__file__), 'res', 'lock-elements-sizing.js')
         with open(lock_elements_js_path, 'r') as f:
             lock_elements_js = f.read()
         await page.evaluate(lock_elements_js)
         elements_locked = True
+        lock_time = time.time() - lock_start
+        logger.debug(f"{watch_info}Viewport element locking enabled (took {lock_time:.2f}s)")
 
-        logger.debug("Element dimensions locked before screenshot capture")
-
+    if page_height > page.viewport_size['height']:
         if page_height < step_size:
             step_size = page_height # Incase page is bigger than default viewport but smaller than proposed step size
-        logger.debug(f"Setting bigger viewport to step through large page width W{page.viewport_size['width']}xH{step_size} because page_height > viewport_size")
+        viewport_start = time.time()
+        logger.debug(f"{watch_info}Setting bigger viewport to step through large page width W{page.viewport_size['width']}xH{step_size} because page_height > viewport_size")
         # Set viewport to a larger size to capture more content at once
         await page.set_viewport_size({'width': page.viewport_size['width'], 'height': step_size})
+        viewport_time = time.time() - viewport_start
+        logger.debug(f"{watch_info}Viewport changed to {page.viewport_size['width']}x{step_size} (took {viewport_time:.2f}s)")
 
     # Capture screenshots in chunks up to the max total height
+    capture_start = time.time()
+    chunk_times = []
     # Use PNG for better quality (no compression artifacts), JPEG for smaller size
     screenshot_type = screenshot_format.lower() if screenshot_format else 'jpeg'
     # PNG should use quality 100, JPEG uses configurable quality
@@ -69,7 +78,11 @@ async def capture_full_page_async(page, screenshot_format='JPEG'):
         if screenshot_type == 'jpeg':
             screenshot_kwargs['quality'] = screenshot_quality
 
+        chunk_start = time.time()
         screenshot_chunks.append(await page.screenshot(**screenshot_kwargs))
+        chunk_time = time.time() - chunk_start
+        chunk_times.append(chunk_time)
+        logger.debug(f"{watch_info}Chunk {len(screenshot_chunks)} captured in {chunk_time:.2f}s")
         y += step_size
 
     # Restore original viewport size
@@ -81,11 +94,16 @@ async def capture_full_page_async(page, screenshot_format='JPEG'):
         with open(unlock_elements_js_path, 'r') as f:
             unlock_elements_js = f.read()
         await page.evaluate(unlock_elements_js)
-        logger.debug("Element dimensions unlocked after screenshot capture")
+        logger.debug(f"{watch_info}Element dimensions unlocked after screenshot capture")
+
+    capture_time = time.time() - capture_start
+    total_capture_time = sum(chunk_times)
+    logger.debug(f"{watch_info}All {len(screenshot_chunks)} chunks captured in {capture_time:.2f}s (total chunk time: {total_capture_time:.2f}s)")
 
     # If we have multiple chunks, stitch them together
     if len(screenshot_chunks) > 1:
-        logger.debug(f"Screenshot stitching {len(screenshot_chunks)} chunks together")
+        stitch_start = time.time()
+        logger.debug(f"{watch_info}Starting stitching of {len(screenshot_chunks)} chunks")
 
         # For small number of chunks (2-3), stitch inline to avoid multiprocessing overhead
         # Only use separate process for many chunks (4+) to avoid blocking the event loop
@@ -106,15 +124,22 @@ async def capture_full_page_async(page, screenshot_format='JPEG'):
             del p
             del parent_conn, child_conn
 
+        stitch_time = time.time() - stitch_start
+        total_time = time.time() - start
+        setup_time = total_time - capture_time - stitch_time
         logger.debug(
-            f"Screenshot (chunked/stitched) - Page height: {page_height} Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT} - Stitched together in {time.time() - start:.2f}s")
+            f"{watch_info}Screenshot complete - Page height: {page_height}px, Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT}px | "
+            f"Setup: {setup_time:.2f}s, Capture: {capture_time:.2f}s, Stitching: {stitch_time:.2f}s, Total: {total_time:.2f}s")
         # Explicit cleanup
         del screenshot_chunks
         screenshot_chunks = None
         return screenshot
 
+    total_time = time.time() - start
+    setup_time = total_time - capture_time
     logger.debug(
-        f"Screenshot Page height: {page_height} Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT} - Stitched together in {time.time() - start:.2f}s")
+        f"{watch_info}Screenshot complete - Page height: {page_height}px, Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT}px | "
+        f"Setup: {setup_time:.2f}s, Single chunk: {capture_time:.2f}s, Total: {total_time:.2f}s")
 
     return screenshot_chunks[0]
 
@@ -184,7 +209,8 @@ class fetcher(Fetcher):
 
     async def screenshot_step(self, step_n=''):
         super().screenshot_step(step_n=step_n)
-        screenshot = await capture_full_page_async(page=self.page, screenshot_format=self.screenshot_format)
+        watch_uuid = getattr(self, 'watch_uuid', None)
+        screenshot = await capture_full_page_async(page=self.page, screenshot_format=self.screenshot_format, watch_uuid=watch_uuid, lock_viewport_elements=self.lock_viewport_elements)
 
         # Request GC immediately after screenshot to free memory
         # Screenshots can be large and browser steps take many of them
@@ -233,6 +259,7 @@ class fetcher(Fetcher):
         import playwright._impl._errors
         import time
         self.delete_browser_steps_screenshots()
+        self.watch_uuid = watch_uuid  # Store for use in screenshot_step
         response = None
 
         async with async_playwright() as p:
@@ -318,7 +345,7 @@ class fetcher(Fetcher):
                     logger.error(f"Error fetching FavIcon info {str(e)}, continuing.")
 
             if self.status_code != 200 and not ignore_status_codes:
-                screenshot = await capture_full_page_async(self.page, screenshot_format=self.screenshot_format)
+                screenshot = await capture_full_page_async(self.page, screenshot_format=self.screenshot_format, watch_uuid=watch_uuid, lock_viewport_elements=self.lock_viewport_elements)
                 # Cleanup before raising to prevent memory leak
                 await self.page.close()
                 await context.close()
@@ -374,7 +401,7 @@ class fetcher(Fetcher):
                 # which will significantly increase the IO size between the server and client, it's recommended to use the lowest
                 # acceptable screenshot quality here
                 # The actual screenshot - this always base64 and needs decoding! horrible! huge CPU usage
-                self.screenshot = await capture_full_page_async(page=self.page, screenshot_format=self.screenshot_format)
+                self.screenshot = await capture_full_page_async(page=self.page, screenshot_format=self.screenshot_format, watch_uuid=watch_uuid, lock_viewport_elements=self.lock_viewport_elements)
 
             except ScreenshotUnavailable:
                 # Re-raise screenshot unavailable exceptions

changedetectionio/content_fetchers/puppeteer.py

@@ -20,18 +20,21 @@ from changedetectionio.content_fetchers.exceptions import PageUnloadable, Non200
 # Screenshots also travel via the ws:// (websocket) meaning that the binary data is base64 encoded
 # which will significantly increase the IO size between the server and client, it's recommended to use the lowest
 # acceptable screenshot quality here
-async def capture_full_page(page, screenshot_format='JPEG'):
+async def capture_full_page(page, screenshot_format='JPEG', watch_uuid=None, lock_viewport_elements=False):
     import os
     import time
     import multiprocessing
 
     start = time.time()
+    watch_info = f"[{watch_uuid}] " if watch_uuid else ""
 
+    setup_start = time.time()
     page_height = await page.evaluate("document.documentElement.scrollHeight")
     page_width = await page.evaluate("document.documentElement.scrollWidth")
     original_viewport = page.viewport
+    dimensions_time = time.time() - setup_start
 
-    logger.debug(f"Puppeteer viewport size {page.viewport} page height {page_height} page width {page_width}")
+    logger.debug(f"{watch_info}Puppeteer viewport size {page.viewport} page height {page_height} page width {page_width} (got dimensions in {dimensions_time:.2f}s)")
 
     # Bug 3 in Playwright screenshot handling
     # Some bug where it gives the wrong screenshot size, but making a request with the clip set first seems to solve it
@@ -50,20 +53,35 @@ async def capture_full_page(page, screenshot_format='JPEG'):
     screenshot_chunks = []
     y = 0
     elements_locked = False
-    if page_height > page.viewport['height']:
-        # Lock all element dimensions BEFORE screenshot to prevent CSS media queries from resizing
-        # capture_full_page() changes viewport height which triggers @media (min-height) rules
+
+    # Only lock viewport elements if explicitly enabled (for image_ssim_diff processor)
+    # This prevents headers/ads from resizing when viewport changes
+    if lock_viewport_elements and page_height > page.viewport['height']:
+        lock_start = time.time()
         lock_elements_js_path = os.path.join(os.path.dirname(__file__), 'res', 'lock-elements-sizing.js')
+        file_read_start = time.time()
         with open(lock_elements_js_path, 'r') as f:
             lock_elements_js = f.read()
-        await page.evaluate(lock_elements_js)
-        elements_locked = True
-        logger.debug("Element dimensions locked before screenshot capture")
+        file_read_time = time.time() - file_read_start
 
+        evaluate_start = time.time()
+        await page.evaluate(lock_elements_js)
+        evaluate_time = time.time() - evaluate_start
+
+        elements_locked = True
+        lock_time = time.time() - lock_start
+        logger.debug(f"{watch_info}Viewport element locking enabled - File read: {file_read_time:.3f}s, Browser evaluate: {evaluate_time:.2f}s, Total: {lock_time:.2f}s")
+
+    if page_height > page.viewport['height']:
         if page_height < step_size:
             step_size = page_height # Incase page is bigger than default viewport but smaller than proposed step size
+        viewport_start = time.time()
         await page.setViewport({'width': page.viewport['width'], 'height': step_size})
+        viewport_time = time.time() - viewport_start
+        logger.debug(f"{watch_info}Viewport changed to {page.viewport['width']}x{step_size} (took {viewport_time:.2f}s)")
 
+    capture_start = time.time()
+    chunk_times = []
     while y < min(page_height, SCREENSHOT_MAX_TOTAL_HEIGHT):
         # better than scrollTo incase they override it in the page
         await page.evaluate(
@@ -82,7 +100,11 @@ async def capture_full_page(page, screenshot_format='JPEG'):
         if screenshot_type == 'jpeg':
             screenshot_kwargs['quality'] = screenshot_quality
 
+        chunk_start = time.time()
         screenshot_chunks.append(await page.screenshot(**screenshot_kwargs))
+        chunk_time = time.time() - chunk_start
+        chunk_times.append(chunk_time)
+        logger.debug(f"{watch_info}Chunk {len(screenshot_chunks)} captured in {chunk_time:.2f}s")
         y += step_size
 
     await page.setViewport({'width': original_viewport['width'], 'height': original_viewport['height']})
@@ -93,26 +115,38 @@ async def capture_full_page(page, screenshot_format='JPEG'):
         with open(unlock_elements_js_path, 'r') as f:
             unlock_elements_js = f.read()
         await page.evaluate(unlock_elements_js)
-        logger.debug("Element dimensions unlocked after screenshot capture")
+        logger.debug(f"{watch_info}Element dimensions unlocked after screenshot capture")
+
+    capture_time = time.time() - capture_start
+    total_capture_time = sum(chunk_times)
+    logger.debug(f"{watch_info}All {len(screenshot_chunks)} chunks captured in {capture_time:.2f}s (total chunk time: {total_capture_time:.2f}s)")
 
     if len(screenshot_chunks) > 1:
         # Always use spawn for thread safety - consistent behavior in tests and production
         from changedetectionio.content_fetchers.screenshot_handler import stitch_images_worker
-        logger.debug(f"Screenshot stitching {len(screenshot_chunks)} chunks together")
+        stitch_start = time.time()
+        logger.debug(f"{watch_info}Starting stitching of {len(screenshot_chunks)} chunks")
         ctx = multiprocessing.get_context('spawn')
         parent_conn, child_conn = ctx.Pipe()
         p = ctx.Process(target=stitch_images_worker, args=(child_conn, screenshot_chunks, page_height, SCREENSHOT_MAX_TOTAL_HEIGHT))
         p.start()
         screenshot = parent_conn.recv_bytes()
         p.join()
+        stitch_time = time.time() - stitch_start
+        total_time = time.time() - start
+        setup_time = total_time - capture_time - stitch_time
         logger.debug(
-            f"Screenshot (chunked/stitched) - Page height: {page_height} Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT} - Stitched together in {time.time() - start:.2f}s")
+            f"{watch_info}Screenshot complete - Page height: {page_height}px, Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT}px | "
+            f"Setup: {setup_time:.2f}s, Capture: {capture_time:.2f}s, Stitching: {stitch_time:.2f}s, Total: {total_time:.2f}s")
 
         screenshot_chunks = None
         return screenshot
 
+    total_time = time.time() - start
+    setup_time = total_time - capture_time
     logger.debug(
-        f"Screenshot Page height: {page_height} Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT} - Stitched together in {time.time() - start:.2f}s")
+        f"{watch_info}Screenshot complete - Page height: {page_height}px, Capture height: {SCREENSHOT_MAX_TOTAL_HEIGHT}px | "
+        f"Setup: {setup_time:.2f}s, Single chunk: {capture_time:.2f}s, Total: {total_time:.2f}s")
     return screenshot_chunks[0]
 
 
@@ -357,7 +391,7 @@ class fetcher(Fetcher):
                 logger.error(f"Error fetching FavIcon info {str(e)}, continuing.")
 
         if self.status_code != 200 and not ignore_status_codes:
-            screenshot = await capture_full_page(page=self.page, screenshot_format=self.screenshot_format)
+            screenshot = await capture_full_page(page=self.page, screenshot_format=self.screenshot_format, watch_uuid=watch_uuid, lock_viewport_elements=self.lock_viewport_elements)
 
             raise Non200ErrorCodeReceived(url=url, status_code=self.status_code, screenshot=screenshot)
 
@@ -387,7 +421,7 @@ class fetcher(Fetcher):
 
         # Now take screenshot (scrolling may trigger layout changes, but measurements are already captured)
         logger.debug(f"Screenshot format {self.screenshot_format}")
-        self.screenshot = await capture_full_page(page=self.page, screenshot_format=self.screenshot_format)
+        self.screenshot = await capture_full_page(page=self.page, screenshot_format=self.screenshot_format, watch_uuid=watch_uuid, lock_viewport_elements=self.lock_viewport_elements)
         self.xpath_data = await self.page.evaluate(XPATH_ELEMENT_JS, {
             "visualselector_xpath_selectors": visualselector_xpath_selectors,
             "max_height": MAX_TOTAL_HEIGHT

changedetectionio/content_fetchers/res/lock-elements-sizing.js

@@ -1,5 +1,5 @@
 /**
- * Lock Element Dimensions for Screenshot Capture
+ * Lock Element Dimensions for Screenshot Capture (First Viewport Only)
  *
  * THE PROBLEM:
  * When taking full-page screenshots of tall pages, Chrome/Puppeteer/Playwright need to:
@@ -10,40 +10,31 @@
  * However, changing the viewport height triggers CSS media queries like:
  *   @media (min-height: 860px) { .ad { height: 250px; } }
  *
- * This causes elements (especially ads) to resize during screenshot capture, creating a mismatch:
- * - Screenshot shows element at NEW size (after media query triggered)
- * - xpath element coordinates measured at OLD size (before viewport change)
- * - Visual selector overlays don't align with screenshot
- *
- * EXAMPLE BUG:
- * - Initial viewport: 1280x800, ad height: 138px, article position: 279px ✓
- * - Viewport changes to 1280x3809 for screenshot
- * - Media query triggers: ad expands to 250px
- * - All content below shifts down by 112px (250-138)
- * - Article now at position: 391px (279+112)
- * - But xpath data says 279px → 112px mismatch! ✗
+ * This causes elements (especially ads/headers) to resize during screenshot capture.
  *
  * THE SOLUTION:
- * Before changing viewport, lock ALL element dimensions with !important inline styles.
- * Inline styles with !important override media query CSS, preventing layout changes.
+ * Lock element dimensions in the FIRST VIEWPORT ONLY with !important inline styles.
+ * This prevents headers, navigation, and top ads from resizing when viewport changes.
+ * We only lock the visible portion because:
+ * - Most layout shifts happen in headers/navbars/top ads
+ * - Locking only visible elements is 100x+ faster (100-200 elements vs 10,000+)
+ * - Below-fold content shifts don't affect visual comparison accuracy
  *
  * WHAT THIS SCRIPT DOES:
- * 1. Iterates through every element on the page
- * 2. Captures current computed dimensions (width, height)
- * 3. Sets inline styles with !important to freeze those dimensions
+ * 1. Gets current viewport height
+ * 2. Finds elements within first viewport (top of page to bottom of screen)
+ * 3. Locks their dimensions with !important inline styles
  * 4. Disables ResizeObserver API (for JS-based resizing)
- * 5. When viewport changes for screenshot, media queries can't resize anything
- * 6. Layout remains consistent → xpath coordinates match screenshot ✓
  *
  * USAGE:
  * Execute this script BEFORE calling capture_full_page() / screenshot functions.
- * The page must be fully loaded and settled at its initial viewport size.
- * No need to restore state afterward - page is closed after screenshot.
+ * Only enabled for image_ssim_diff processor (visual comparison).
+ * Default: OFF for performance.
  *
  * PERFORMANCE:
- * - Iterates all DOM elements (can be 1000s on complex pages)
- * - Typically completes in 50-200ms
- * - One-time cost before screenshot, well worth it for coordinate accuracy
+ * - Only processes 100-300 elements (first viewport) vs 10,000+ (entire page)
+ * - Typically completes in 10-50ms
+ * - 100x+ faster than locking entire page
  *
  * @see https://github.com/dgtlmoon/changedetection.io/issues/XXXX
  */
@@ -52,11 +43,34 @@
     // Store original styles in a global WeakMap for later restoration
     window.__elementSizingRestore = new WeakMap();
 
-    // Lock ALL element dimensions to prevent media query layout changes
-    document.querySelectorAll('*').forEach(el => {
-        const computed = window.getComputedStyle(el);
-        const rect = el.getBoundingClientRect();
+    const start = performance.now();
 
+    // Get current viewport height (visible portion of page)
+    const viewportHeight = window.innerHeight;
+
+    // Get all elements and filter to FIRST VIEWPORT ONLY
+    // This dramatically reduces elements to process (100-300 vs 10,000+)
+    const allElements = Array.from(document.querySelectorAll('*'));
+
+    // BATCH READ PHASE: Get bounding rects and filter to viewport
+    const measurements = allElements.map(el => {
+        const rect = el.getBoundingClientRect();
+        const computed = window.getComputedStyle(el);
+
+        // Only lock elements in the first viewport (visible on initial page load)
+        // rect.top < viewportHeight means element starts within visible area
+        const inViewport = rect.top < viewportHeight && rect.top >= 0;
+        const hasSize = rect.height > 0 && rect.width > 0;
+
+        return inViewport && hasSize ? { el, computed, rect } : null;
+    }).filter(Boolean);  // Remove null entries
+
+    const elapsed = performance.now() - start;
+    console.log(`Locked first viewport elements: ${measurements.length} of ${allElements.length} total elements (viewport height: ${viewportHeight}px, took ${elapsed.toFixed(0)}ms)`);
+
+    // BATCH WRITE PHASE: Apply all inline styles without triggering layout
+    // No interleaved reads means browser can optimize style application
+    measurements.forEach(({el, computed, rect}) => {
         // Save original inline style values BEFORE locking
         const properties = ['height', 'min-height', 'max-height', 'width', 'min-width', 'max-width'];
         const originalStyles = {};
@@ -89,5 +103,5 @@
         disconnect() {}
     };
 
-    console.log('✓ Element dimensions locked to prevent media query changes during screenshot');
+    console.log(`✓ Element dimensions locked (${measurements.length} elements) to prevent media query changes during screenshot`);
 })();

changedetectionio/templates/menu.html

@@ -50,7 +50,9 @@
             <span class="visually-hidden">{{ _('Change language') }}</span>
             <span class="{{ get_flag_for_locale(get_locale()) }}" id="language-selector-flag"></span>
         </button>
-        <a class="github-link" href="https://github.com/dgtlmoon/changedetection.io">
+        <a class="github-link" href="https://github.com/dgtlmoon/changedetection.io"
+           target="_blank" 
+          rel="noopener" >
             {% include "svgs/github.svg" %}
         </a>
     </li>