Have you sought assistance in the beta mailing list? https://thunderbird.topicbox.com/groups/beta Or filed a bug? https://bugzilla.mozilla.org/home

But perhaps you need to reconsider this statement.

All of the explanations I have seen online to fix this problem do not have any applicability in this version!

Hyperlink handling is not something that changes much. I don't recall more than 1 or 2 changes in the last 10 years. So what makes you think that? Is it you can't find the config editor in the newly renamed "Settings" on the menu (It has had three names in three major versions)

About 10 years ago I wrote this article and it is as valid today as it was when I wrote it as it has had a few updates in that time. Have you seen it?

Hello Matt and all,

  First off, Happy New Year!  Since you celebrated the new year yesterday and we won't do so till midnight tonight, I hope my wish isn't too belated.
  My problem with links is a bit strange.  When a link is embedded within the text of an Email I can access the link in Firefox with no problem.  The issue is though if the link is in the form of an attachment it is a no-go.  It doesn't matter what I try to do with it...double clicking doesn't work, bringing up the dialog box and hitting "Open" doesn't work.  And, I have yet to find any way of fixing it.
   Thank you for the suggestion about contacting the beta mailing list.  I will have to do that.
           John