I’ve been using late betas and RCs for a while now and like what I see. It has a nicely minimal interface and seems quite a bit faster than Firefox 3. It still doesn’t load as quickly as Chrome 10 on older hardware, but Firefox is a champ, and is still my favourite all-around web browser. Best of all: Firefox 4.0 is available for Linux, Mac, and Windows (yes, even XP.) to say nothing of smaller, lesser-known operating systems and platforms. (Firefox for Android seems to be progressing nicely.)
Congratulations, Mozilla. I look forward to your shorter development cycles.
(Now, don’t forget Thunderbird. It’s feature-complete to me but could certainly use some belt tightening.)
Here’s to an open, standard, and competitive web!