You might have to do an uninstall and go through the registry and remove all elements if Firefox before reinstalling. Firefox does have a funny way of ending up with weird errors occasionally as I remember several years ago it started swapping images for no particular reason, eg: a Smiley would become someones avatar (at the 100px x 100px size) and a signature image would condense down into the Smileys dimension and appear even in the page formatting. To say the least, it was one really weird bug.

Anyways a clean reinstall fixed that and maybe you'll have to do the same thing because this has been going on for a while now and I'm unaware of any others with the same issue. :confused