Mozilla Firefox is a versatile web browser that offers numerous features to enhance users' browsing experience, including the ability to manage bookmarks efficiently. While Firefox doesn't natively provide a feature to display duplicate bookmarks within its library, there are several methods and add-ons you can utilize to achieve this functionality.

You would need to use an add-on. In a quick search, this one had strong reviews and a large enough user base to think that the reviews are reliable:

https://addons.mozilla.org/firefox/addon/bookmark-dupes/

I have not used it myself (although I should!!)

On the author's github, you can submit issues and get direct assistance if needed. This was one of the more interesting tips I saw there:

How to detect that an http address and https address are duplicates: https://github.com/vaeth/bookmarkdupes/issues/109

P.S. If you want to make an extra "just in case" bookmark backup before using clean-up tools, Firefox has two formats and I recommend doing both:

• JSON Backup: Restore bookmarks from backup or move them to another computer
• HTML Export: Export Firefox bookmarks to an HTML file to back up or transfer bookmarks

Hopefully you won't need those.

Splendid. Worked fine. Many thanks. If you dug this out of the ether, you are a talent. I've fiddled around on web for days to find such apps. I would hope Mozilla could bank such repairs into the HELP section - I am obviously not the first one to be bothered by dupes in the bookmarks.