Deseja configurar um "link para o aplicativo" no menu de contexto como este
[Desktop Entry]
Comment=
Exec=firefox -new-window http://unix.stackexchange.com/questions/151004/how-do-i-get-a-desktop-in-kde-to-open-a-new-browser-window
GenericName=
Icon=exec
MimeType=
Name=Stackexchange
Path=<whereever you want>
StartupNotify=true
Terminal=false
TerminalOptions=
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=
X-KDE-SubstituteUID=false
X-KDE-Username=