I had almost precisely this problem. When I attempted to upgrade to FF3 (YaST was showing a 3.0.1 version available in S/W Management), the dependency tracker added the xulrunner. But when this attempted to download, it timed out. I clicked “Skip” and it installed everything else, but then running FF3 failed as you describe.
I fixed it by going back to YaST, searching for xulrunner 1.9.0 and installing that on its own. Then everything was fine.