Doing a little research, it appears that Node.js isn't supported on SPARC because V8 doesn't have a SPARC backend. That does seem like it will make it impossible to build Firefox on SPARC once the Node.js requirement is established :/
We knew some lesser-used platforms might run into problems like this. For Solaris, it should still be possible to cross-compile Firefox to SPARC from x86. So I don't believe the Node requirement will mean the end of Firefox on Solaris SPARC.
0:27.19 checking for nodejs... not found
0:27.20 WARNING: could not find Node.js executable; ensure `node` or `nodejs` is in PATH or set NODEJS in environment to point to an executable
0:27.20 WARNING: (This will become a fatal error in the near future.)
Is it necessary to make it hard requirement for Firefox build? It might be quite problem to get Node.js for Solaris and mainly for sparc.