“Writing applications that work in all different browsers is a friggin’ nightmare. There is simply no alternative but to test exhaustively on Firefox, IE6, IE7, Safari, and Opera, and guess what? I don’t have time to test on Opera. Sucks to be Opera. Startup web browsers don’t stand a chance.
What’s going to happen? Well, you can try begging Microsoft and Firefox to be more compatible. Good luck with that. You can follow the p-code/Java model and build a little sandbox on top of the underlying system. But sandboxes are penalty boxes; they’re slow and they suck, which is why Java Applets are dead, dead, dead …”
Taken from Joel Spolsky’s Strategy Letter VI.
It’ll take five minutes of your time and it will be time well spent.