What about 32-bit binaries?  I built Mozilla 0.7 on Solaris 2.6 and 7,
 the binaries are both

 /usr/local/src/X/mozilla-source-0.7/SunOS5.7/xpfe/bootstrap/mozilla-bin:
 ELF 32-bit MSB executable SPARC32PLUS Version 1, V8+ Required, dynamically \
 linked, not stripped

One option you have is to install the NetBSD/sparc snapshot with a 32-bit
NetBSD/sparc64 kernel.  You may have some KVM issues, but compat SVR4 works
rather well in that conviguration.

Eduardo