Firefox displaying weird text formatting

I'm using Firefox 1.5.0.4 on Windows XP. Quite suddenly Firefox has
started rendering text on many webpages almost in an almost unreadable
way. This doesn't seem to happen in any other application. What happens
is text is displayed overlapping on other text--here is a screenshot to
better explain this:

http://i112.photobucket.com/albums/n...trendering.jpg

That's actually a fairly readable example. I've looked in Firefox's font
options and don't see anything out of the ordinary. I also don't think
XP is causing the problem since this doesn't happen with other browsers
or any other applications. Though I'm willing to check or change
whatever someone might recommend to solve this.

I've also tried uninstalling and then reinstalling with no extensions,
but that had no effect. This problem happens on many different sites,
sometimes affecting only small parts of the page, sometimes nearly
everything. And it also doesn't happen at all on many sites.

Anyone have any ideas?

Todd Brassman