Comment 5 for bug 367354

My /var/lib/dpkg/alternatives/xulrunner was empty.

So I did "sudo rm /var/lib/dpkg/alternatives/xulrunner"

then reinstalled xulrunner-1.9.1 (like: sudo apt-get install xulrunner-1.9.1 )

then ... purged xulrunner-1.9.1 ( sudo apt-get purge xulrunner-1.9.1 )

Now everything is fine