Firebird is creeping slowly but surely towards 1.0 with the 0.7 release. I very quickly moved from IE6 to Firebird without any major loss of functionality — indeed, I’ve gained functionality versus IE, a browser I’ve faithfully used for years. I also migrated from Outlook Express 6 to Mozilla Thunderbird with nary a problem in sight, and that was migrating to a 0.1 version!
‘functionality versus IE’ gives a 404
Ah, holy crap, they moved stuff around after I posted – try http://website-beta.mozilla.org/products/firebird/compare/