Lets you keep a BIG number of tabs open without getting lost in the list. This is as close as I've found to a replacement for Tab Groups. Thanks to one of the "improvements" in the new FireFox, it seems you can't actually have hidden tabs, but with this extension you can arrange tabs in a collapsible hierarchy like an outline in MS Word, so the sidebar shows only the ones you want immediately available. (All tabs still show up in the tab bar at the top of the page.) I was using Tree Style Tabs for a while, until I realized that it wasn't a preference I had set wrong: that extension actually doesn't have a tab search.

Overall, this is just plain great. It's why FireFox is my main browseer.

But still…

• When I save a session with a lot of container tabs, they reopen as ordinary tabs — meaning, if I understand the documentation, all the usernames, cookies etc. I've been keeping for separate user IDs are suddenly visible to every site. (If you just quite FF with preferences set to restore windows/tabs, the container IDs *are* preserved.

• Search function should open any tab currently hidden by collapsing higher levels of the tree. Right now you can't see any hits in collapsed tabs, or in groups other than the current one

• Container tabs should show their container color

• Auto-collapse (hides other stuff when you expand a branch of the tree) should collapse only at the highest level, so that one click redisplays that branch as it was before you opened a different one. At the moment, this function collapses everything. If you have a top-level tab with 20 descendants at three different levels, you only see direct children when you reopen