View Full Version : Massive Performance Hit since Firefox 15

5 Sep 2012, 1:20 AM
Anyone else noticed that Firefox 15 seems to run some things unbearable slow?

E.g. Panel Headers and Toolbars in autoScroll:true enabled Containers (e.g. TabPanels). When they are out of viewport and scroll them back in they take a 3 second long timeout until they reappear.
Makes my whole app a pain to use.

Firefox 14 was much much faster.

5 Sep 2012, 2:22 AM
haven't noticed any difference...

either way, have you minimised your panel nesting?

5 Sep 2012, 7:55 AM
Yeah it's not that. Panel nesting is minimized to the bone.
Downgraded to Firefox 14 and got no issues anymore on Mac & Windows.
It's mostly even just a rendering glitch that results in Text not being visible when CSS gradients are set as background.

After a few second of Guru-Meditation the text reappears (no Browser resize or JS doLayout stuff required that would point to the typical overnesting issues).

5 Sep 2012, 8:11 AM
Quick comparison, same machine.
First with FF 14


Then same machine after installing the update to FF15


8 Sep 2012, 1:55 AM
In case anyone stumbles over this issue as well.

I've just found a workaround for this Firefox glitch.
The cause is related to the z-index that is defined as such:

.x-docked {
position: absolute !important;
z-index: 1;

Firefox 15 has a regression when something like this is inside a containing element that uses "overflow:auto" that has at the same time no value set to its "z-index" property.

To fix this all i had to do is make sure the containing element gets a z-index of any value (except 'none');

.x-panel-body-default {
z-index: 0;

15 Oct 2012, 10:40 AM
Great find! I am gonna try this fix out. My app has become stupid slow in Firefox.