On Sun, Aug 5, 2018 at 08:21 AM, Lena wrote:

There is an extension for that:
https://addons.mozilla.org/ru/firefox/addon/remove-visited-link/

But perhaps not really viable for the "less IT- savvy", IMHO

However, I just spotted another way of achieving the desired goal. (I think!)

• Identify the post that requires a "follow - up" rather than an immediate answer.
• Click on "Reply".
• Refresh the page.
  The "typing area" that appeared when clicking on Reply will disappear, and a "Drafts" tab will appear on the left hand side.
• Go away and do something else; the Drafts tab will still be there later when you come back, whenever that happens to be.
• Open the draft (or the first of several) and complete the reply. When all the Drafts have been dealt with the tab will go away.

OK the flag is "Drafts" rather than "Follow - up" but it's a much more positive indication than reverting the thread topic to "blue".

Chris