Does anyone use this add-on?

(you need an account to see links)

For the longest time, it has stopped working in later FF version. Does anyone know of an alternative extension that works the same - allows multiple profiles for browsing with diff. profiles whenever you want to switch around. Or if they know a fix for this? I tried it on another computer and it works fine in the latest version, so it's only my computer it isn't working on. I tried debugging/disabling all extensions but still no way of narrowing down the issue.