If you're seeing strange fonts appearing after upgrading to Firefox-4, here's the quick fix:
- Go to your profile folder's chrome folder (in Windows XP, e.g. C:\Documents and Settings\your xp username\Application Data\Mozilla\Firefox\default\chrome
- Open file UserContent.css with a text editor (or create a new empty text file with this name if it doesn't already exist)
- Add one new line to this file:
- @font-face { font-family: 'helvetica neue'; src: local('Arial'); }
- Save file.
- Restart Firefox.
Enjoy the your Firefox-4 (which is sadly slower and buggier than earlier ones but what can you do?)