The modern Internet simply is just too resource heavy for PowerPC Macs. I commend people like Cameron Kaiser for having spent a lot of time and effort to keep it accessible through efforts like TFF, but I feel for general use, the boat has truly sailed well over half a decade ago usability wise.
And that's mostly because the modern web is a bit of a pig, but then it has also gotten far more advanced than it ever was in 2005 and before. If you want to browse the 'net on a vintage machine, there's still a few great retro sites to go to. Wiby is a search engine for suitably retro sites, Cornica is a video site for Macs as old as the faster 68040 machines, etc. The modern 'net just needs modern hardware, and it's only going to get heavier.