Looks like you fixed it. Usually I find that happening the exact opposite - looks fine in FF and in IE it drops something below the div next to it. That's usually when I don't have the floats set properly or the divs are too big width-wise to fit on the screen.

I'm seeing the drop in both Mozilla and IE at 800 by 600 resolution. mattbta's right: Normally it's IE that drops sidebars, but either way you've got too much space expected for the pixels available. Generally speaking you have to be way off to get Mozilla (or FF or other 'worthy' browsers) to do the drop when IE doesn't, so it's possible you've got significant issues in your css.

Does your xhtml and css validate? It's always a good place to start - valid xhtml allows the css validator to run, and valid css *implies* that a standards-compliant browser will display as desired.

Take a look at your "bPosts" and "bPost" and "bSideBar" and "bSideItem" divs. Are you using percentages for widths? If so try shaving one or two percent off them. Also look at your margins and paddings (focusing on lefts and rights) - they all have to add up to the number of pixels available or else the sidebar gets dropped down to where it fits. If you are using ex or em those guys will change with screen resolution. I have a skin that uses percents for bPosts and bSideItem that add up to 92% in order to not drop the sidebar on lower resolutions. It's my margins and paddings that take up the other 8% of 800 pixels.

Drop a percentage point here, reduce an em or ex there, maybe even shave a few pixels off px values and eventually it'll all pop into place. Well, until someone comes along with 800 by 600 resolution and font size set to "supersize it" and turns on one of the browser sidebar things, but you can only go so far to make it 'right'.

Thanks for your help guys. I'm using percentages to set the column widths, I've never used em or ex, but I guess its time to read up on them and see if they'll work better for what I'm trying to achieve.

My percentages added up to 96%. I adjusted both of them down to a total of 92%, and that helped. I guess I need to go through and check all my margins and paddings, because I don't like that wide blank spot between the columns, and eventually I plan to have a 3rd column on the left-hand side as well.

One last question...

Also look at your margins and paddings (focusing on lefts and rights) - they all have to add up to the number of pixels available or else...

How can I tell how many pixels are available, I've always just picked an arbitrary browser size. Is there a way to force it to a particular size?

Thanks,
Chris