Firefox 2.0.0.4 is all I know so cannot comment any short comings of other versions. After using FF for all of 5 days I think its excellent with a better feel than an equivalent version for Windows PC.
The Spell Checker in FF is brilliant much easier than the 'check spelling' icon in Internet Explorer so I can correct my spelling and typo's as I type.
Has anyone tried Thunderbird as a mail client, its from the same people as Firefox and works much better than 'Mail' in OS X.
(Ark at me, Mac commentator)