In which ways has Mozilla attacked Facebook? One way I'm aware of is their "Facebook Container" extension, which is basically the same as their Multi-Containers extension, with the key difference of being preconfigured for Facebook. Last I checked there is a similarly preconfigured extension for Google, but that one is from a 3rd party extension developer, not Mozilla (I have a very hard time recommending 3rd party extensions to other people since I do not know if those extensions will remain trustworthy...)

This suggests to me that improving the UX of the generic Multi-Container extension should be a higher priority. As it stands, doing something as simple as creating a new container for a site and then having that site always open in that container takes numerous less-than intuitive user actions.

1) Click "+" (tooltip: create new container)

2) Fill out a name for the container, and choose from a very limited choice of colors and icons (only 8 colors and 12 icons; 96 total combinations)

3) Open a new tab with that container, and navigate back to the website

4) Select "Always open in [container name]"

5) Open a new tab, nagivate back to the website

6) Select "Remember my decision"

7) Select "Open in [container name]"

Step 2 should not have such inane artificial restrictions. Step 3 should happen automatically. Step 6 and 7 should not happen at all because my choice in Step 4 should be respected.