Site works in all browsers but Firefox 1.5 (macOSX)

Hey all:

so i used browsertest to check a simple page. it works in all pages except with firefox 1.5 for mac OSX. any ideas? just the background doesn’t show up. it’s kinda odd. here’s the link:

http://mark-stuckert.net/TestBook/

any help would be appreciated!

thx,
decisionman