You should check out "Simple Tab Groups". You can bind tabs of a certain group to always open in a specific container. On top of it you get fantastic grouping, and hiding of tabs in groups, and other controls. In this way I have container groups segmented to their own views and have no issues controlling how existing logins work between different use cases. It's also easy to back up and share between machines.

https://addons.mozilla.org/en-US/firefox/addon/simple-tab-gr...