Firefox 1.5 has been released, and is available for download at http://www.mozilla.com/firefox/. While superficially it looks like nothing has changed, there are some huge improvements hidden just below the surface.
All of these are fantastic to see - Firefox really is blazing its own path now, no longer caught in the no-win situation of simply following Microsoft's lead. Of course Firefox has been better at standards conformance and nuances of CSS for some time, but that doesn't really inspire a lot of end-user adoption - it's the features that matter, and in that domain it has taken a hefty lead (including over anything I've seen with IE 7).
I've been using Opera 8 as my primary browser for several months, after a couple of years with Firefox as my mainstay. Given some of the improvements I think I'm going to switch back.