The last time I checked, a number of the plugins I rely on were still incompatible with Firefox 3. However, I'm hoping that will be sorted out before the final version is released.
Irrespective of whether that happens, I'll still get involved with Firefox Download Day.
Yes, it's really just a little silly, but what other chance am I every likely to have to get involved in a Guinness World Record attempt?
Of course, the actual date hasn't been announced yet, but if you follow the link, you can register to be alerted once it has been decided.