So only one group would be expanded, and to change to a tab in another group you would expand that group and then choose a tab, and the group you left would collapse? I can't think of any built-in feature for that. Mozilla has a product suggestion site at https://connect.mozilla.org/. If you have time, I think it would be a good idea to post this request there to get into the current feedback stream. Use the "Ideas" section of the site (at https://connect.mozilla.org/t5/ideas/idb-p/ideas).