fix(video-quality-label): push around z-indexes for firefox

css/_vertical_filmstrip_overrides.scss

@@ -22,10 +22,10 @@
          * clickable but its inline dialogs must display over the video state
          * indicator when videos are displayed.
          */
-        z-index: $tooltipsZ;
+        z-index: #{$tooltipsZ + 1};
 
         &.hide-videos {
-            z-index: calc(#{$tooltipsZ} - 1);
+            z-index: #{$tooltipsZ - 1};
         }
 
         /**

css/modals/video-quality/_video-quality.scss

@@ -142,11 +142,14 @@
     }
 }
 
-#videoResolutionLabel,
 .centeredVideoLabel.moveToCorner {
     z-index: $tooltipsZ;
 }
 
+#videoResolutionLabel {
+    z-index: #{$tooltipsZ + 1};
+}
+
 .centeredVideoLabel {
     bottom: 45%;
     border-radius: 2px;