I'd try a couple of things.

First, try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

You will need to restart Firefox for this to take effect so save all work first (e.g., mail you are composing, online documents you're editing, etc.,) and then perform these steps:

1. Click the menu button and select Options (Windows) or Preferences (Mac, Linux).
2. Select the General panel.
3. Under Performance, uncheck Use recommended performance settings. Additional settings will be displayed.

   

4. Uncheck Use hardware acceleration when available.
5. Close Firefox completely and then restart Firefox to see if the problem persists.

If the problem keeps happening, you may want to try simply reinstalling Firefox. You should be able to install over your current installation without losing any data. This would make sure that there is nothing corrupt or damaged in your Firefox program.

NOTE: To protect your personal settings and data, it's recommended that you backup your Firefox profile before reinstalling Firefox. See Back up and restore information in Firefox profiles for more information.

Disabling hardware acceleration did nothing to help. I suppose I'll reluctantly re-install Firefox, but there's no way in HELL I should have to!

Ok, let us know how it goes. Sometimes it's just a case of a file getting damaged from a change in another software or Windows update or something along those lines.

There's really not any risk to installing over top of your current version of Firefox, since the installer doesn't touch your Firefox data at all.

Hopefully that will fix the issue for you.