Difference between Safari and Firefox

I viewed the website I made in dreamweaver on Survivor (http://mywebspace.quinnipiac.edu/jmgrado/survivor_home.html) in Safari and Firefox. I found minor differences, but even though they're minor they can throw off any website. In safari, everything was laid out as I wanted it to be, except for some unexplainable white space on a page. In firefox, the menu and the bottom of the site were a few pixels away from where i wanted them to be. I find this as a problem because what is a client uses firefox? The designer could have made a great website that looks fantastic in Safari, but in firefox it could look unorganized and ugly. Another thing, is that a blue box appears around the button in firefox, whereas in safari, there is none.