If my font-family is set to Arial the Text in FF/IE/Safari looks similar. But if I set it to Georgia the Text in Safari differs strongly from the text in FF/IE.
That's probably Safari's anti-aliasing doing that. Text won't render the same on all browsers, so it's easier to let that one go instead of trying to fight it.
I agree what kari.patila said in his above comment. I just to add to his solution I have given the url below, which explains more about why the font differs in the different browsers.