@Ed Davis... about bookmarks... can you try the https://addons.mozilla.org/firefox/addon/close-unused-blank-tabs-plus/

Otherwise great addon, but unfortunately author is AWOL. :(

This has worked flawlessly for me for many months, but now on Firefox 60 something is malfunctioning.
When I run the browser, it opens with an empty tab, from the New Tab Override extension, which is set to open new tabs with "about:blank". If I click on a bookmark, a new tab opens as I have Firefox set to open bookmarks in a new tab in the "about:config" settings. Correctly, Close Unused Blank Tabs then shuts the first tab.
Unfortunately, what happens now is that if I then close the tab I opened with the bookmark, a blank tab reappears as Firefox is not set to close when the last tab is closed, which then sticks there, and new tabs then always open beside it and Close Unused Blank Tabs does not remove it as it used to.
I don't know whether this behaviour is because of a Firefox update or something else. It used to work fine, always closing empty tabs, but now it no longer seems to.
Any ideas anyone?

There needs to be a way to cancel this action when I am opening multiple tabs at the same time. Otherwise, this works great.

Now causes problems when you use "Open all in tabs" from right-click menu on bookmarks folder - only one tab remains opened, the rest are closed automatically by this extension. When you click on several bookmarks in quick succession to open them in new tabs, many of them are also closed immediately. Otherwise great extension and thanks for many years of service!

Hi,
First, thanks for this great addon !
Is that possible to add an option to close also the active blank tab ?
Thanks in advance.

My use case :
Sometimes when I open a file (like a PDF for example), a blank tab is opened and the file is opened with external program (like Adobe Reader for PDF).
But the blank tab stays open et becomes the active tab, so I have to close it to return to the previous tab.
So, if the extension can closes active blank tab, I can return to previous tab automatically.