Looks like a font issue.

You can do a check for corrupted and duplicate fonts and other font issues:

• http://www.thexlab.com/faqs/multipleappsquit.html - Font Book 2.0 Help: Checking for damaged fonts
• http://www.creativetechs.com/iq/garbled_fonts_troubleshooting_guide.html

When I started Firefox this morning, it acted like it was going to freeze again, but finally showed an alert with the option to continue/stop a script which was running. I don't know what page it thought it was working with, since it was supposed to be starting a new session, but whatever it was, stopping the script seems to be working. I will still check out the font issue to see if that is contributing to any problems, though. Thanks!