I don't believe there is a solution for this, unless you write a plugin for firefox, that also
implement all the client stuff for the samba protocol.
With Konqueror it is working, because the way KDE works, firefox is not an smb client as far
as I know. With kde you can add protocols that are used by all KDE-aware applications, but
firefox is not a KDE application, I think it is possible to rewrite it that way since it has been
done with mozilla in the past to be a html-engine for Konqueror.