A coworker had this problem. After installing a plugin-update, the fonts on her Firefox interface were all italic. We combed over the preferences to no avail, then a simple Google search revealed the answer.
- Open Font Book
- Find Lucida Grand Regular
- Right Click > Reveal in Finder
- Delete it. AAHHHHH!!!! Yes, I’m sure, delete it,
- Witness the true power of a fully operational Mac Station, it suddenly recreates the font for you. Amazing
Now of course you need to restart Firefox, and everything was cool.
Did this help you out? It took me a few days to piece together all this information together, I hope this saves you some time (who knows, maybe the future me will be thankful I wrote this down). Let me know your thoughts. email@example.com