I had an absolute struggle to manage my dev workload between the Container tabs, bookmarks, and environments, so this add-on is an absolute godsend.

I cannot believe how I managed to survive without it, and really haven't looked back since.

It beggars belief that this functionality is still not baked into Firefox.

UPDATE: I should've updated sooner, now that Firefox finally has this built-in. However, I still prefer this add-on because, for me, it maintains the colour scheme of the containers.