Hmmmm, I haven't used 10.3 in a while, but for 10.2 I use Opera 9.64. Massive swapping aside, Tiger ran ok on my 300MHz/512 WallStreet, so don't knock it until you try it. I think the last version of Firefox for 10.3 is 2.x.x and somewhere there are some nice CPU optimized builds of it.

EDIT- I couldn't find the nice page, but here is a link to the archive (pre FF3) http://firefoxmac.furbism.com/builds/archive/G3/

I think this is that last one that is 10.2 compatible: http://firefoxmac.furbism.com/builds/archive/G3/FX2-G3-2.0.0.14.dmg