Earlier quoted context omitted.
"Yes, in principle I could export the list of tabs to a text file, and begin anew ..." I came here to complain that, actually, you can't . Or rather, it's surprisingly complicated to export a simple list of current tab URLs to a plain old text file. You need to dig several directories deep into /Library (or whatever, depending on your OS) and then use JSON tools to export ... I've already lost most people. Why can't…
For Firefox, there is Export Tabs URLs.
about:tabs would be the easiest thing in the world.