You've made me think about what it must be like to try old software on my machine. Hmmm....
EDIT: Done! I just ran the oldest version of Firefox I could on this machine, version 220.127.116.11 (released April 13, 2006). It's no PS1 but it'll do.
Here are a few interesting screenshots:
Evidently, Firefox doesn't trust its origin.
I didn't realize that Firefox was up to date (the problems with linking to a page that is not version specific). Interesting...
Google's homepage renders okay (it is a fairly simple design after all).
Apple...not so much (it is a fairly complex page).