Hey Mikal, I used Explorer for the Amsterdam presale without problems. I used it for the Amsterdam general sale, too, with success. You don't need Firefox, nor would I necessarily use it instead of Explorer if you have Firefox already installed.
In my typically paranoid delusional state, I also turned off my Zonealarm firewall, AVG and Pop Up Stopper, in case they delayed my connection by a tenth of a second, which sometimes makes all the difference. I also cleared out my temp files folder, did a full computer scan with AVG, Spybot and Adaware and turn all unecessary background processes using Windows Task Manager.
Total overkill, I know, but I have this fear that my comp will freeze, some virus or malware will slow me down or some scanner will automatically turn on right in the middle of a ticket sale.
During the Amsterdam general sale, I couldn't get an internet connection 30 minutes before the sale began... called my ISP, etc., turned out my modem was dead.. went to a friends' house at 2:20am after to use their computer after wasting an hour, but lost 40 crucial minutes, very aggravating
- lucked out and got 3 A'dam 2 GAs anyway after three hours of refreshing, but that was a major drag - good luck!