In an attempt to get an outbreak of sweetness and light (hopeless, I know), may I make the following points
- It could be, but probably isn't, an explicit microsoft conspiracy. Its more likely 'cockup' than 'conspiracy'; I'd bet no testing has been done on various lower-market-share browsers and configurations and that has allowed something nasty to creep in rather than a deliberate attempt to sabotage anything (but I could be wrong)
- when its running slowly, could you check how quickly name look ups occur, please? So 'dig www.this.that', and preferably do a similar thing with something that runs at a reasonable speed (google?).
- does it also run slowly if you get something from cache (eg, with the back button)?
- and what about a traceroute to one of the sites in question
and, are you really sure that you have thoroughly excised all references to IPV6? Having a mix of IPV6 and IPV4 seems to be the most common ways of having networking work slowly these days. And what about something untoward in nsswitch.conf? Can you post that, please?