I’m on chrome, but I’m using them through a simple development extension I wrote which examines the url of ungrouped tabs and adds matching tabs to a few predetermined groups that I’ve hard-coded into the JavaScript. It was a quick and dirty hack that took me about 30 min to setup, but it’s made the tab grouping functionality so much more useful.

I’m toying with the idea of adding an options page so that I could release it to the chrome store, but I hate UI work, so I haven’t gotten around to that yet.