Heya semp,
you might be able to go into your C:\HTC\Aces High II\ folder or it might be C:\hitech creations\Aces high\ ( depending on if you changed it or not ) ( also some might still have it in C:\program files\ directory )
anyways.go to your Aces High Folder and right click on the IE shortcut icon listed as "Getting Started with Aces High" then in the Web Document tab add a short cut key pointing toward FireFox
since it shows up as a Internet Explorer icon, it is defaulting to open with IE........ adding the short cut key should solve your problem
hope this helps.... good luck