I'm using a CSS-based tooltip on a page I'm developing, and it displays fine on IE (v8), but on Firefox (v3.6.2) there is an additional 25 pixels or so of padding/margin at the right.

I can't for the life of me work out why, so if anybody wouldn't mind taking a look at the page in question and seeing if they can fix what I'm sure is a relatively simple problem, I'd greatly appreciate it:

As this is my first post, I'm not allowed to post the URL of the page I'm having problems with, so please PM me if you're interested in taking a look.