Let's look forward to Firefox 3.0.
One of the things that has bothered Firefox's creators has been it's inability to pass the Acid2 browser test. A recent alpha release of Firefox 3.0 has been able to pass thanks to changes in it's rendering engine. Now Firefox can pass it will join the likes of Safari and Opera in being able to say it is truely (or at least as near as possible) standards compliant. And, of course this puts them another step ahead of Microsoft with Internet Explorer.