Firefox 3 has been discussed on the OpenBSD ports@ mailing list:
http://marc.info/?l=openbsd-ports&m=121331390107153&w=2
NOTE: This development work is for -current,
only.
There is a possibility that a backport effort to retrofit the port to -stable can produce a functional application. It is even possible that some OpenBSD users might do that work, on behalf of the user community. However, the OpenBSD Project itself will not undertake the effort. The developers do not provide new functionality to -release/-stable, as a matter of policy.