Bug 1763717 - Updated PiP text-tracks bottom multiplier r=kpatenio

Differential Revision: https://phabricator.services.mozilla.com/D143322

toolkit/actors/PictureInPictureChild.jsm

@@ -80,9 +80,6 @@ const TOGGLE_HIDING_TIMEOUT_MS = 2000;
 const SEEK_TIME_SECS = 5;
 const EMPTIED_TIMEOUT_MS = 1000;
 
-// If you change bottom position in texttracks.css, also change this
-const TEXT_TRACKS_STYLE_BOTTOM_MULTIPLIER = 0.066;
-
 // The ToggleChild does not want to capture events from the PiP
 // windows themselves. This set contains all currently open PiP
 // players' content windows
@@ -1415,6 +1412,9 @@ class PictureInPictureChild extends JSWindowActorChild {
     const isReducedMotionEnabled = originatingWindow.matchMedia(
       "(prefers-reduced-motion: reduce)"
     ).matches;
+    const textTracksFontScale = this.document
+      .querySelector(":root")
+      .style.getPropertyValue("--font-scale");
 
     if (isFullscreen || isReducedMotionEnabled) {
       textTracks.removeAttribute("overlap-video-controls");
@@ -1424,8 +1424,7 @@ class PictureInPictureChild extends JSWindowActorChild {
     if (isVideoControlsShowing) {
       let playerVideoRect = textTracks.parentElement.getBoundingClientRect();
       let isOverlap =
-        playerVideoRect.bottom -
-          TEXT_TRACKS_STYLE_BOTTOM_MULTIPLIER * playerVideoRect.height >
+        playerVideoRect.bottom - textTracksFontScale * playerVideoRect.height >
         playerBottomControlsDOMRect.top;
 
       if (isOverlap) {