I'd go with Camino 1.6, but it's 1.8.1.x-era Gecko, so I wouldn't try to do anything secure or high-level with it.

I'm slowly grinding through the Classilla security audit, but that just makes it safe, not necessarily more functional. Still, it's an option for Classic.

Or, get 512MB RAM in it (or more) and run 10.4, and then you have more choices.