Many site issues can be caused by corrupt cookies or cache. In order to try to fix these problems, the first step is to clear both cookies and the cache. Note: This will temporarily log you out of all sites you're logged in to. To clear cache and cookies do the following:

1. Go to Firefox > History > Clear recent history or (if no Firefox button is shown) go to Tools > Clear recent history.
2. Under "Time range to clear", select "Everything".
3. Now, click the arrow next to Details to toggle the Details list active.
4. From the details list, check Cache and Cookies and uncheck everything else.
5. Now click the Clear now button.

Further information can be found in the Clear your cache, history and other personal information in Firefox article.

Did this fix your problems? Please report back to us!

This can be a problem with the font that is used to display the text.

You can use this extension to see which fonts are used for text that is selected (right-click context menu: Show fonts in selection).

• fontinfo: https://addons.mozilla.org/firefox/addon/fontinfo/

You can do a font test to see if you can identify corrupted font(s).

• http://browserspy.dk/fonts-flash.php?detail=1

You can try different default fonts and temporarily disable website fonts to test the selected default font.

• Tools > Options > Content : Fonts & Colors > Advanced
• [ ] "Allow pages to choose their own fonts, instead of my selections above"

I had the same problem and it was fixed by installing the European Union Expansion Font Update. Even if you're not using a European flavor of Windows, this should still fix the problem. Link to Microsoft Download Page