Ok, I'm 99.9% sure now that the problem was being caused by the link mentioned in my previous post, ending in fox.htm and labelled as a flash exploit. Since blocking it and the ip it comes from with firefox addons and internet options I no longer get crashes when visiting worldofraids.com nor any warnings from AVG or avast, although it seems to have been removed from the site anyway.
I've done one final set of scans with avast, avg, MBAM, SUPERAntiSpyware, Spybot S&D, plus a HijackThis log and they've turned up nothing, apart from SUPERAntiSpyware finding the atdmt tracking cookie still.
So anyway, Tarq, thank you very much for all of your help, and my apologies if any of my replies were a bit rambling or unclear. Also, YoKenny, thank you for your recommendations too. And essexboy, thank you for that, if it pops up again I will defiantly give it a go.