My recent experiences with Firefox (1.0.6) have been less than satisfactory; the ForecastFox extension keeps saying that I do not have permissions for some file every time I start Firefox (this started happening after an upgrade of the extension). Firefox also doesn't seem to remember my passwords sometimes. I have switched to Opera for the time being. I was worried that I would miss the Adblock extension, but it turns out that Privoxy does a good job in blocking ads. Such a good job that even the banner ad in Opera is blocked (I am planning to allow Privoxy to display the ad once each session, just to ease my guilt).
I miss the other FF extensions, though - the Gmail/Bloglines notifiers, DictionarySearch and ForecastFox. Opera has a Feeds option that takes care of the notifiers; I can also use kweather for the forecast, which leaves only the dictionary thing.