css/css-contain/content-visibility/content-visibility-068.html

Fix a WPT test relating to `content-visibility: auto` and
content-relevancy. This test attempts to change the relevancy of content
by blurring it, but relevancy also depends on selection. Apparently,
Gecko differs from other browsers in that `blur()` is not moving the
selection as well. The fix is to simply focus another element which will
update both focus and the text selection.

Differential Revision: https://phabricator.services.mozilla.com/D163706

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1797447
gecko-commit: 978147969b8ee70daa1920402b6ad2bc938207ee
gecko-reviewers: emilio

css/css-contain/content-visibility/content-visibility-068.html

@@ -30,6 +30,7 @@
 }
 </style>
 
+<div id=end tabindex=1></div>
 <div class=spacer></div>
 <div id=container>
   <div id=focusable tabindex=0></div>
@@ -79,7 +80,11 @@
       assert_equals(r.y, 3000, "step4 offset");
       assert_equals(r.height, 10, "step4 height");
     });
-    focusable.blur();
+
+    // We don't use `blur()` here because in Gecko this leaves the selection
+    // on _focusable_ which means that its content is still relevant. Focusing
+    // another element will move both focus and selection.
+    end.focus();
     requestAnimationFrame(step5);
   }
   // After blurring the focused element, we should go back to the contained