Try to delete the file urlclassifier3.sqlite to reset the phishing protection database and force Firefox to rebuild a new database file (this can take some time).
You can find the file urlclassifier3.sqlite in the parent location of the cache.
You can see the location of the cache on the about:cache page via the location bar like you access a website.

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Tried your suggestion to create a new profile but it also crashes in the new profile (didn't even transfer the old files). I tried to find the location of the .sqlite file but it crashes before I can finish typing "about:cache"

It looks like it doesn't crash until I've started typing something. I can visit various web pages fine (following links), but try to type something and it crashes.

Any other ideas?

Maybe 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

You can also try some maintenance:

Repair the disk permissions:

• http://thexlab.com/faqs/repairprocess.html
• http://guides.macrumors.com/Repairing_Permissions

Remove the Firefox plist file (org.mozilla.firefox.plist).

• http://www.macfixit.com/article.php?story=20060606082246983 How .plist files become corrupt and troubleshooting the results

Go to "~/Library/Preferences" and remove the plist file for Firefox (org.mozilla.firefox.plist)