Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
Also just wanted to note that you are using version 12.0 and the current release version is 18 and so I suggest that you do an update.
version 18 produces the same result.
you can check to see if this happnes to you by going to http://www.friendsorlandophil.org and clicking the treble cleft image on the right hand side.
That is a problem with the code on that page that has a backslash instead of a forward slash and Firefox interprets the \\www.orlandophil.org as a relative path in the current www.friendsorlandophil.org domain
You can contact the website to inform them about this typo.