Hmmm, I spoke too soon... I was using a restart add-on ("Restartless Restart") to test and restored Tabs were behaving as I hoped (not loading until clicked). But after quiting FF the normal way and relaunching it all Tabs are reloaded in spite
of the fact "Reload all tabs" is deselected in the TBP options (Session/Restore).
Interestingly, if I start a private browsing session then stop it, when it returns from the private session, all tabs reappear with the titles in red italics and they only reload when clicked.
Maybe because Private Browsing turns off the History function? I'll try fiddling around with the settings a little more, but I can't see there's much more the user can do. Hopefully the developers can figure it out (assuming it is
possible...) - certainly be an asset to the app, especially given unnecessay downloading can impact on those with monthly GB limits (the majority I would imagine)
Sorry to get everyone's hopes up!