Gallery Main Page Table Width issue

Hi

I am not sure why in Firefox, my gallery is displayed incorrectly.

I have set the middle, white <div> to have a width of 500px and float left and as far as I am aware, the gallery table is set at 100%.

So why is it on the front page, the gallery has overshot my div and flown out to the right? It is ok when you go into an album.

best Regards

Josh

The following information is required to get an answer:
Get this information from the PHP diagnostic (in the configuration wizard).
Gallery URL (optional but very useful): http://www.union.ic.ac.uk/halls/fisher
Gallery version: 1.5.1
Apache version: 1.3.29
PHP version (don't just say PHP 4, please): PHP v4.3.11
Graphics Toolkit: ImageMagick
Operating system: Linux
Web browser/version (if applicable): Firefox