It works fine, but there's an annoying bug in the OSX version of Firefox. The scroll bar is displayed on top of the "X" icon that closes tabs. I can usually close one tab by clicking the X, but as soon as I do this the scroll bar appears and I can not close any more tabs without moving the mouse cursor outside of the All Tabs Helper menu. This makes it impossible to quicly close several tabs.

Looking at the screenshots on this website the All Tabs Helper menu looks different, with the X button to the left of the scroll bar, so I assume that the behaviour I get is a bug. I couldn't find any other way to contact the maker this addon so I'm writing a review here. I hope it can get fixed.