If you've created several CSS-only layouts, chances are you've tried to make one that looks like this:

-----------
| --- --- |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| --- --- |
-----------

It probably ended up blowing up in Firefox. Sad!

What you need to do is modify your layout so you need a footer:

-----------
| --- --- |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| --- --- |
| |-----| |
| |-----| |
-----------

The footer should have the following style:

{clear: all;}

(it can have any other style you like, and of course you can name the element whatever you like, just it must have the clear: all; directive.)

Easy, huh?