I use Mozilla Firefox 3.0.5 and few days ago it was being closed automatically showing crush report. So, I was unable to work properly. After start browsing it was closed within 20 minutes. I solved the problem using following steps:
1. After uninstalling the failed installation of Firefox 3.01, I still found a Mozilla Firefox directory under C:\Program Files\. I renamed this to old-Mozilla Firefox. This forces the new install to make a new folder. I would try this alone first and see if it works.
2. The second thing that I had done was to use regedit to find and rename all registry entries that seemed to be related to Mozilla Firefox. Again, this forced the new install to make new registry entries.
All the best with your install.