Gah! Pesky div floating problem.

I’m ashamed to be asking for help with this, because it’s a bear to try to track down, I know. I’ve been banging my head against it for a while now, and I’m maybe just hoping that another set of eyes might be able to spot the problem that I’m overlooking.

It’s happening on the single.php page of my theme, and here’s a typical example:
https://rchseaglesnest.org/06-25-2008/around-school/school-news-test-article-number-seven/

I’m trying to get rid of the gap between the bottom of the article content and the top of “Reader Comments”, which looks like it’s clocking in right after the content in the sidebar is finished.

The sidebar has a fixed width and is set float: right, so I can’t for the life of me understand why the main content doesn’t just flow up and “lock” together.

I’m certain I have no loose </div>s floating around — everything matches up. I’ve tried rearranging the location of the sidebar in my code, but that seems to be a bad idea.

Can anyone spot the problem?

Thanks!
Jeff.

(Oh. Firefox only, for now — I haven’t started debugging IE yet; not sure what I’ve got going on over there yet!)