Talk about your beta releases. IJlogin currently works for switching between accounts. Huzzah!
On the downside, logging out of the IJ website doesn't change the statusbar widget, even though it should. Logging out of the widget after logging out the site produces an "Invalid password" error on perfectly good passwords. Vexing! I'm looking into it. For now, try to log in and out through IJlogin and you shouldn't have any problems.
Tested on: Firefox 18.104.22.168, 22.214.171.124 - 126.96.36.199 (all on WinXP)
I'm looking for bug reports and non-XP operating system reports. If you have a problem with IJlogin, especially if you're not on Windows XP, please reply!