I do love this add-on. However, if you are adding this to an already used window with multiple tabs, you should make sure to add ALL current tabs to new groups BEFORE you attempt to switch to a new group. I lost a few hundred tabs and using History, spent two weeks trying to re-find those lost tabs. A good idea for multiple tabs would be an add-on similar to "Copy All Tabs Urls WE" 1.0.4 By Michele Pezza - at least you won't lose your tab's addresses.