Hi,
I just ran a test with Firefox 3.0.5 (latest) on XP-SP3 and no problem with the new bulk Auctiva Uploader. I'm also running the Java JRE version 1.6.0_11 (latest), which is required for the uploader for non-ActiveX browsers/systems.
http://www.java.com/en/download/manual.jsp
Do you have the Java Runtime Env. installed?
Danno