This feature is so elementally useful, I am surprised that I have to add it as an extension. It seems like it should be a default feature. It is also one of the primary reasons I exclusively use Firefox. For a while I was happy to use Chrome exclusively because it provided what I needed and the synchronization or backup of each instance was very helpful. Since that doesn't cross web browsers, I only switched because Firefox, lately performs better and has this feature to increase my security, privacy, and account management ability. It doesn't take extra time to deal with these issues because I just have a few pinned tabs with the right container in them. It's awesome.