Oh jeez, I think I follow. It's either simple or out of my range. We have "open links in new tab" in FF, but not so for following tabs. So if the original window had a link, you clicked it, it opened a tab, that new tab is really treated as a new window when it's active. So in my mind, the tab opened from the first window must be aware that it's a tab...or a second window.
This would be a great add-on for an enthusiast, so that's sparked me a bit. Grandpa's usage though is the actual problem here and I have to stop developing right now
So...turn off "new tabs in links". Then any links clicked "open in current window". It's minor education either way you look at it...and tabs are a bit tough to chew on. If you click something, you move away. If you want to go back, use the back button. FF is good with that, and I'm with ya on teaching tabs....it's just too much. So as a mediator, kill that nice tab function and show them the back button.
In teaching those around me in even basic functions of Windows and browsers; it really is just like an actual desktop. "how do I move this?" Well, you just grab it, and move it over. Tabs are hard to fit into that world (Damn Post-It Tabs) because tabs are stacking papers on a desk. It's all papers on a desk and tabs are...tabs. Start with a desk...a real desk. Put papers on them and show how it's the same thing, but easier.
I'm just thinking of teaching my parent.