Problem setting firefox default browser KDE 4.3.1

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?