To be specific, after I used the guest account on my XP system for the first time, and Firefox was used (well, technically my roommate did the surfing, and it wasn't "Guest", it was another account with guest privs), Firefox on my login suddenly started caching pages inappropriately. Namely, even though I had the cache size set to 0, my friends page wasn't showing updates when updates happened. (I tested this by viewing /friends?skip=0.)
I had to clear the cache before the page would start updating, and after I cleared the cache, I had to continually clear it each time I wanted the page to be checked again each time. Finally, I figured it out, went into the guest account, and set Firefox to cache = 0 (from 5000), and all my troubles went away. At least, all my browser troubles. Well, most of them. Firefox still doesn't like PopCap Games' content.