UPDATE:
I really need the containers to be grouped (for easier access and management), manually sorted and bookmarked with container information attached to be easily restored.
I am developing a web site. I have test users with their roles on site. For each user I created an individual container. 6 roles require 6 pages to be restored every time I reload the browser. I want them be restored automatically in their respective container at the time when the Bookmark was created. One site, several bookmarks with individual containers for each test user/role.

ORIGINAL REVIEW 2 years ago
I used to open Chrome for one Google account and Firefox for another. To check business emails on Gmail and to view videos on YouTube, for example. It consumed quite a lot of resources on my old Dell Vostro 3700. Now, I can manage all my "personas" in Firefox alone, which I personally like more.

But, the new "problem" now is it's hard to find necessary tab on Windows task panel. So, I suggest, that not only individual tabs can be marked as containers, but every FireFox window could be assigned a default "persona" with different coloring and EVEN logo (I like the Fox, but sometimes it'd be useful to have those personalized icons to faster localize necessary tabs). PS. I use A LOT OF tabs (up to 50 in one session, I guess). So, saving time trying to locate a necessary tab would be cool.
On the whole, this is a really cool feature which is worth taking time to understand how to use. Firefox, please make a new button - Learn the Feature - so that it would be like an ed course with games, videos and tests (reading is boring and confusing, as you know).