Over at MacOSXHints Rob G has written a useful and interesting review in the Spotlight Article: Firefox: Mozilla successfully rethinks its browser. Subsequent discussion also points to the extraordinarily useful Web Developer extension for Mozilla Firefox and Mozilla which adds a menu and a toolbar to the browser with various web developer tools.
I’ve been messing around with FireFox for a few days now and am impressed. I’m using it alongside Safari and would happily recommend it.
As for the Developer toolbar, well, how useful and fun! Instant validation, highlighting all the block-level elements, replace images with alt attributes – I could while away many an evening with this.