I think you're talking about the Mozilla Accounts feature (recently renamed from Firefox Accounts). It is not as smooth an experience as Google accounts, but i

I think you're talking about the Mozilla Accounts feature (recently renamed from Firefox Accounts). It is not as smooth an experience as Google accounts, but it works reasonably well. Firefox has a separate profile feature, and it is one of the great things about Firefox. You can access profiles through "about:profiles". You can (at least on Linux, don't think it's possble on MacOS) start firefox with a profile chooser. Each profile is a completely isolated browser instance -- no shared bookmarks, cookies, history, anything.