On my G3 devices (I tried on a 500 MHz iBook Dual USB from 2001), PowerFox crashes a lot while it doesn't on my G4. Both have the same amount of RAM (640 MB vs. 768 MB), so this should not be the issue. Still I am impressed that you got PowerFox running on the G3. Btw, I did not try yet on my iMac G3 Lime (400 MHz), nor the iBook G3 Clamshell SE (466 MHz) ... (just checked the correct MHz number).
My personal webpages are truly made for old computers, they might be slow to render, but I always make sure that at least TFF/InterWebPPC/Aquafox can display them in a way you can read all information nicely (not all effects applied, and may be some glitches here and there). No unnecessary scripts, no Google analytics, no search enginge optimization, and still find my own stuff can be found when needed.
May be we should abandon the modern web and create our own - well as we did in the beginning - with the same spirit of frogfind dot com.
To replace sites like Meta's "The Social Network", most forums offer additionally Social Network capabilities, e.g. macrumors has space for images, profiles, PNs, it's truly a social media platform, just with a focus to news, and public conversations (forum).