Bug 1723188 - Hide hidden animated images in about:preferences using display: none in addition to visibility: hidden to avoid having them use CPU. r=preferences-reviewers,jaws

Differential Revision: https://phabricator.services.mozilla.com/D121398

browser/themes/shared/preferences/preferences.css

@@ -361,6 +361,12 @@ checkbox {
   visibility: hidden;
 }
 
+/* Work around bug 560067 - animated images in visibility: hidden
+ * still eat CPU. */
+#updateDeck > *:not(.selected) > .update-throbber {
+  display: none;
+}
+
 #updateDeck > hbox > button {
   margin-block: 0;
   margin-inline-end: 0;