All of a sudden, my firefox crashed on me, and every time I try to re-open it, it keeps on crashing.
I tried everything on here: http://support.mozilla.org/en-US/kb/Firefox%20cras
You can do a check for corrupted and duplicate fonts and other font issues:
Even if you haven't installed new fonts yourself then it is still possible that one or more fonts aren't working properly, so you can still test them with the Font Book application just to be sure.
Try to disable hardware acceleration in Firefox.
The "Use hardware acceleration" was already checked, so I unchecked it. It still doesn't seem to do the trick... Am I out of hope?
How do I check for corrupted fonts? I clicked on those two links and I couldn't figure out what to do (i'm really technologically slow)
I had this problem too, so just in case I ran a Malware scanner, it found and removed some questionable files and so far Firefox seems to be working as normal again.
I used Malwarebytes http://www.malwarebytes.org/products/ which is free. I don't think they have a Mac version though and even though you're on a Mac, it might be worthwhile to scan for malware. Do a search for a Mac malware scanner, there will probably be a free versions out there.