Very well done. By far the best extension I've ever used. Does exactly what it needs to do. This extension is one of the main reasons I no longer use Chrome. Finally I can have multiple YouTube accounts signed in instead of having to pull up a private browsing window. The features it add should be added to regular Firefox. My suggestion is that they add the ability to have a default container that all tabs open in, and be able to set up multiple containers that begin already open when you launch Firefox.