fireworks displays my theme in a slightly different way. why?

hello,
Browsing on fireworks, my theme does not look like how i designed. the main menu is shifted.

what should i do to make my theme look exactly the same as it looks on explorer. Somehow the main menu on top of the page looks a bit shifted from the real page when i view the site with fireworks. whereas with explorer it was ok.

What should i do to make my theme look good in both web browsers. I designed my theme on explorer view , is it why it looks strange on fireworks?

if i did the browsing on fireworks when designing the theme, would the theme look good on explorer as well. Could you please clarify the problem.

Thank you in advance