Dear users: Please ignore the advice of this well-intentioned but
poorly-informed poster. There's no such Firefox version as "3.*.*",
3.0.* works for this usage.
If you want to run GM in FF3.0RC1 please install this RC1 of GM 0.8:
http://arantius.info/gm/greasemonkey-0.8.20080505.0.xpi
This would be the publicly available build, but Aaron (the lead
developer) appears to be MIA. I'm rather sure he'll have it up on AMO
once he's back.