Coming from Opera, this add-on is a godsend for an alternative to workspaces, functioning just as you'd expect. It isn't without its minor flaws, though: When clicking the icon for the extension, it always opens up the list of tabs in the current group first, forcing an additional click to see the list of groups. The only benefit you get that isn't already on the top of the Firefox window is quicker access to customizing the current group, which is way less useful than quickly changing which group you're in, the main point of the add-on. Plus, the icons you can set for groups are very limited in design, and it seems weird that you can't at least use the icons for containers. But again, this add-on performs flawlessly and helps productivity immensely, so I still recommend it.