[bug 876072] Overlays on mobile should stay fixed

media/less/mobile/main.less

@@ -390,7 +390,7 @@ input[type="submit"]:visited {
   background: rgba(40, 40, 40, 0.98) url('../../img/grain.png') 0 0 repeat;
   bottom: 0;
   left: 0;
-  position: absolute;
+  position: fixed;
   right: 0;
   top: 0;
   z-index: 100;