Performance issues in Firefox 39 beta

[tyaremco]

In Firefox 39 I experience periodic jank (browser hangs) every 1-2min lasting 5-15s each.

• When I disable uBlock Origin (9.8.1.1) the symptoms disappears.
• I'm not doing anything in particular when the issue occurs (can happen multiple times on a static page)
• I have not experienced this issue in Firefox 38 or below
• my Firefox session has hundreds of tabs, however the issue presents itself with only a few tabs loaded (ie. nearly all of the tabs are pending/unloaded)
• I first noticed this 1 month ago when I was testing Firefox 39 dev version.

I was able to narrow down the culprit by running the Gecko Profiler Addon. I can upload my performance profile if you need it. Here is a section of the timeline where I experienced the issue and the offending stack traces:

It seems that vAPI.tabs.getAll() is responsible for the majority of the running time...

[tyaremco]

I can confirm that the same problem exists for chrisaljoudi/uBlock 0.9.4.

[gorhill]

Thank you very much for the report. This might also be the reason for #252 -- though it was FF 38.0.5.

[tyaremco]

The fix appears to be working great!

I maintain several Firefox bugs related to large numbers of tabs so I keep a setup such that these situations are easy for me to test. I'll test #252 and see if I can get some useful information for you if it's not fixed.