CSS not ok with Firefox / Safari

My Divs are displayed correctly only with IE, firefox does not render properly, why ?

The thing is... it was ok, and suddenly, it's not.
Look at this page
http://www.hopitel.com/hopweb_fre.html
The two black buttons are not at the same place under firefox...
Why ?

Thanks for helping.

you have an huge maze of divs and relative positioning (with margins) going on there. it would take ages to work out what's actually going on. BUT - the problem is this image: http://www.hopitel.com/images/texttiming.gif There's about a 50px transparent gap at the bottom fo that image which pushes the buttons down the page. Firefox is doing what it should be doing, it's IE that's not working properly. If I were you, I'd break it all down and re-code the entire page as 3 (maybe 4) divs. Instead of putting lots of images together, make a few bigger background images and position your text over it...