[Firefox] uBlock button breaks Firefox app menu

[jimporter]

This occurs on Windows 7 with Firefox 36.0 under a fresh profile. I wasn't able to reproduce on Linux.

Steps to reproduce:

1. Install uBlock (I tried with 0.8.8.2, 0.8.8.4, and 0.8.8.5-dev.3)
2. Customize the Firefox toolbars and drag the uBlock button to the app menu's popup (the thing with the 3 lines)
3. Navigate to a page where uBlock would block something
4. Try to open the app menu: it slides open and then immediately closes

[ZeldaZach]

Doesn't appear to affect FF 36 Mac OSX 10.10.2

[Deathamns]

Duplicate of #638.