I realy love this extension, it's what I always searched for!
One feature that I'd love to see is the ability to map containers with firefox accounts.
By that I mean I have a personal firefox account with a set of bookmarks and a professional one.
Firefox containers kind of overlap with firefox accounts. On one hand I can access all my bookmarks and on the other one I can separate concerns easily.

Maybe I'm missing something but that would be awesome instead of going about:profiles everytime.