I can view this thread on OmniWeb 3.0 running on OpenStep 4.2 (screenshot proof) but I can't post because OmniWeb lacked JavaScript support and reddit heavily depends on that.
This is 1999 software, but really it dates back more to 1997 (there were some patches after that, 1997 was when Apple bought NeXT).
FWIW, OmniWeb is now up to version 5, and the codebase runs on OS X, the successor to OpenStep.
Omniweb still supports OS X 10.4 (Tiger), which is what I assume you're running.
You should also be able to upgrade to OS X 10.5, and be able to run the latest versions of Firefox, Chrome & Opera.