Found a great little tutorial that fixes the problem (it's a PhotoBucket issue - new codes):
Just get the "Find And Replace" Firefox Add-On and you're set (you'll find links to everything in the above tutorial).
All I had to do was change the "s100" in the URLs to "i100". Fixed!
Have no idea why the same mood themes are working just fine in Chrome, but oh well.
Just thought I'd pass along the link in case anyone else was having this problem.