Very nearly what I'm looking for... the only thing I really want is to have tab groups visible in the sidebar in an accordion style rather than groups that you need to "move into". I would like to be able to see all tabs across multiple (or all) groups in the sidebar at once - I don't mind how exactly this is implemented behind the scenes, it could still use group context switching and such when I click between tabs in different groups. But being able to open and see tabs from multiple groups at once would provide feature parity with tab grouping in other browsers (not to mention all the extra features this addon provides on top of that), especially now that we can use the sidebar effectively as a replacement for the default Firefox tab list.