Note: This is for Windows only. I have not seen this happening on Mac or Linux.
Firefox 4 takes advantage of hardware acceleration to quickly display web pages. What happens is while the page is loading it looks like, but once it finishes loading it looks like this example below:
Character Encoding issue caused by Firefox 4 use of hardware acceleration and an incomplete/damaged Windows Font Cache
This issue is caused by the Windows Font Cache either being incomplete or damaged. The fix is fairly simple. NOTE: You must be logged into Windows as admin in order to perform these steps:
1. Close Firefox
2. Type services.msc into the Start Search bar (or from the run prompt) and hit Enter.
3. Find the Windows Font Cache Service, select it and hit Stop.
4. Open Windows Explorer and go to C:\Windows\ServiceProfiles\LocalService\AppData\Local * requires admin privileges *
5. Delete the FontCache dat files. (They will be regenerated over time.)
6. Restart the Windows Font Cache Service.
7. Open Firefox.
