Your page doesn't begin with a complete <!DOCYTPE>, so browsers will render the page in what's called "quirks mode" - and every browser works differently in that mode. You want to use a complete <!DOCTYPE> statement so that browsers will render your pages in "Standards Compliance Mode" so that they'll all at least try to render the pages using the same rules. There'll still be differences, but they're trivial when compared with Standards/Quirks modes.
Search on "doctype switch" and you'll find some good advice.
