Just a word of caution, anecdotely I installed the Container extension/feature 2 weeks ago when this was discuted on HN, I opened some tabs in different contexts, copied important links I wanted to keep, then decided to hide them, then finally yesterday I wanted to read one of these links, I go look in the menu... Pouf gone, all my links gone... Least to say I was happy.. Therefore not only I have uninstalled this feature but also Test Pilot altogether. I decided from now on to keep things simple because it seems this is only what really works. Maybe I'm rambling a bit, but the sad truth is I don't have much trust in Firefox anymore, I use it because it is to me the least worst browser, not because I really enjoy using it.