Try posting at the Web Development / Standards Evangelism forum at MozillaZine. The helpers over there are more knowledgeable about web page development issues with Firefox.
http://forums.mozillazine.org/viewforum.php?f=25
You'll need to register and login to be able to post in that forum.

Be sure to add a link to that website in your post.
Firefox uses a default margin of 8px in the body. If you do not want that margin then add this style rule:

body {margin: 0px}

There may be other difference depending on the DOCTYPE that you specify (or omit).

After hours and hours of removing code and content, I finally figured out why it is jumping from one page to another (and it's a bit embarrassing to admit): the %!&#? scroll bar's absence or presence shifts the page that many pixels to the right and left!!! This doesn't happen in IE because it is always there, whether used or not. Does anyone know how to "fix" this "problem" in Firefox? I think it looks really clunky for it to jump left and right depending on which page on my site you click on.

You can force a vertical scroll bar with body {overflow-y: scroll}

Thanks for the tip cor-el. That solved my problem! Looks much better now.

You're welcome