I've been using this add-on for about a year now, and while it's hit some typical development roadbumps, it is a fundamental part of my browsing experience. It is simply a fantastic tool for organizing the hundreds of tabs I have at any given time, and backing them up as bookmarks is a fantastic bonus feature. I think there's a reason this add-on has been designated as "recommended" by Mozilla/Firefox - I wouldn't be surprised at all if they were looking at bringing the features of this add-on into the main FF codebase. IT'S THAT GOOD, REALLY!