Comment by JoshMnem

> My standing solution is to use one browser to log into big-G services, another to log into FB, and a third for everything else.

Check out Firefox container tabs.[1] You can isolate sites within one browser and save the associations between containers and tabs.

I use container tabs along with multiple Firefox profiles (for different combinations of browser extensions).

[1] https://support.mozilla.org/en-US/kb/containers