It's very annoying all these standards. As Mick says - Firefox, Safari and Chrome are the leading ones in terms of "standards". Internet Exploder is the odd one out with it's archaic interpretation of what it thinks the world wide web standards should be
Each browser provider has their own interpretation of how things ought to be done - even though all prescribe to the World Wide Web Consortium (a not-for-profit organisation that aims to standardise web standards). I use Safari nearly exclusively but annoyingly there is one or two websites that only run on Internet Exploder - which being a Mac user renders me unable to use them at home.