firefox: Add org.kde.kdeconnect to plasma integration comment (#6285)

I recently set up KDE connect and plasma-browser-integration for firefox
(Linux Mint 21.2) and needed this line in addition to the ones mentioned
in the profile. Found it via running `firejail
--profile=/etc/firejail/firefox.profile --dbus-user.log firefox`, trying
to send links to device, and seeing what events get logged.

etc/profile-a-l/firefox.profile

@@ -55,6 +55,7 @@ dbus-user.own org.mpris.MediaPlayer2.firefox.*
 # Add the next lines to your firefox.local for plasma browser integration.
 #dbus-user.own org.mpris.MediaPlayer2.plasma-browser-integration
 #dbus-user.talk org.kde.JobViewServer
+#dbus-user.talk org.kde.kdeconnect
 #dbus-user.talk org.kde.kuiserver
 # Add the next line to your firefox.local to allow screen sharing under wayland.
 #dbus-user.talk org.freedesktop.portal.Desktop