Since you've failed to show the issue, I'll guess that you're using that new sidebar option that I'm not. I can right on one of my other devices and open all the tabs. see screenshots

Thank you for replying so quickly!

My problem was that nothing happened when I right clicked on any of the lists of tabs (whether on the side bar or elsewhere) "open" on the other device. I don't know why.

However, I solved my problem by using the "Tab Session Manager" extension. Exporting the list to a USB drive which I then put in the device I wanted to move the tabs too. Then importing that file. The only trick is that one has to pin the extension to the FireFox toolbar to have access to the tabs and windows, which is done by clicking on the clipboard type of icon up by the three horizontal bars on the (almost) top right. (I wrote that in case someone else has a similar problem and is looking for a solution.)

So thank you again, Stephen.

Great. Mark this issue resolved to remove it from our list and have a nice day.