Nice. Now my wife and I can both stay logged in to our email. I've wanted this feature for 15 years. Now, bring multi row tabs back and FF will be awesome again.
Have you considered just creating multiple windows/mac accounts? Since you can switch without having to log off, it's really convenient. I understand partners sharing accounts and such but it's really just a better workflow/experience IMHO.
That's what I've always done when I don't want to use multiple accounts on the machine itself.
[0]https://support.mozilla.org/en-US/kb/profile-manager-create-...