As I posted previously, I had some problems with the new version of Firefox.
So today, first day back at work, I installed the update (Firefox 0.9.1).
After this new installation I still had the same problems related to the default browser behaviour.
Solution: this registry patch
Next problem was that it was still opening new windows from external programs.
Solution: the single window extension
…now I’m fine. Happy browsing. Still, these issues should be solved in a next release.