Yes, I have several Firefox profiles. There are 7 profiles on WinXP Pro SP3 between 6 Windows user accounts and 4 on my Win7 SP1 machine between 3 Windows user accounts. I've tried all the troubleshooting modes listed for Firefox, including disabling all other extensions and then restarting Firefox. On the profiles where WebRep doesn't work, even that doesn't help.
What's weird is that the wrc*.json files in the profiles where WebRep doesn't work were updated when that profile was used. That indicates that WebRep is probably running but there is no visible clue of that in the Firefox interface. In some profiles, the WebRep icon on the Navigation Toolbar would show (greyed out) until starting to load the first site and then even it would disappear. Of course, now those files haven't updated since uninstalling WebRep.
For now, I'm keeping WebRep disabled. When AIS 8 is officially released, I'll do a clean install of it although I still think that there is something in those profiles stopping things up. If it persists, I'll likely rebuild those profiles from scratch and then move over the password files, bookmarks, permissions, etc. None of prefs.js, etc as that is likely where the problem lies.