Merge pull request #15889 from timdream/lockscreen-transitionz

Bug 966711 - Use translateZ() for lockscreen fade-out transition, r=snowmantw

apps/system/style/lockscreen/lockscreen.css

@@ -11,7 +11,7 @@
      that we might be slow at the beginning of the transition. */
   transition:
     transform 0.5s cubic-bezier(0.7, 0.0, 1.0, 1.0),
-    opacity 0.5s cubic-bezier(0.7, 0.0, 1.0, 1.0),
+    opacity 0.5s cubic-bezier(0.7, 0.0, 1.0, 1.0);
 }
 
 #screen.active-statusbar > #lockscreen {
@@ -20,7 +20,11 @@
 }
 
 #lockscreen.unlocked {
-  transform: scale(2);
+  /* Workaround specifically targetting Gecko:
+     The transform here is equal to scale(2),
+     however this will stop Gecko from creating a 2x big layer (4x the memory),
+     resulting super-smooth transition. */
+  transform: perspective(1000px) translateZ(500px);
   opacity: 0;
   pointer-events: none;
 }