Hi,
I wrote a new WebExtension for bookmark management.
With the Bookmarks Organizer, it’s easy to put order in your bookmarks. The Bookmarks Organizer finds no longer working bookmarks, redirects, duplicates and more!
The Bookmarks Organizer is a WebExtension and also compatible with Firefox 57 and later.
Features
Finds no longer working bookmarks Finds duplicate bookmarks Finds bookmarks without name Broken bookmarks can be edited or deleted Detects redirects and offers the automatic correction of individual or all redirects
Shortcuts
The interface can also be accessed via the keyboard. For this purpose the combination Ctrl + Shift + L (macOS: Cmd + Shift + L) is reserved.
It is also possible to start individual tests directly via the address bar:
bookmarks organizer: opens the interface bookmarks duplicates: search for duplicates bookmarks empty-names: search for bookmarks without name bookmarks errors: search for broken bookmarks bookmarks redirects: search for redirects
Planned features
There are already some features planned for the future.
Whitelist: create exceptions for bookmarks, which will no longer be objected to during further checks Features for bookmark folders, including empty folders & more…
Languages
The extension is currently available in the following languages:
English German Dutch (Thanks, Tonnes!) Czech (Thanks, MekliCZ!) Polish (Thanks, WaldiPL!) Upper Sorbian (Thanks, milupo!) Lower Sorbian (Thanks, milupo!)
It’s not yet reviewed (still on position 478 in the queue) but in the meantime the add-on could be improved. 
AMO page:
You can find the code repository here:
If someone wants to contribute (new features, bugfixes, translations or typo fixes) please send a pull request. Maybe we can make the add-on better before it will be available for the masses. 
There will be an update for New Tab Override after the release of Firefox 54. 