I've just updated to latest kde 4.3.1 from factory repo.
After this when I'm trying to open any link at kopete or plasma widgets i get an error dialor:

KDEInit cannot start !/usr/bin/firefox.:
Could not find '!/usr/bin/firefox' executable.
Changing default browser back to Konqueror makes the trick and link are opened by Konqueror.

Any ideas how to make it start firefox?