It occurred to me that Shin'ichiro TAYA wrote in gmane.os.netbsd.devel.toolchain:
> If nobody running NetBSD-3.0/amd64 and can't confirm my fix on 3.0 in a 
> few days, I'll  commit them.

I'm running a bulk build right now (Which I expect to be finished within the 
next few hours). After that, I'll happily try to build (and run) firefox in a
3.0 chroot.