No user interface, no instructions, absolutely nothing to guide use of this extension, rendering it useless. I'd like to know how those users who are giving high ratings managed to use this.

This extension has no instructions and no intuitive interface; in fact it has no interface or way to execute it at all.

No controls: no menu add-ons, no rh-click context sensitive button, nothing. It might work well if only I could figure out how to run it...

I installed this in Android Firefox I disabled all my other add-ons and this 404 bookmarks did nothing. No results. nada

This app needs options to slow it down and to pause the search. its causing my browser to crash and not allowing me to use google due to my email bookmarks activity!

Detects 404 page though the URL is a correct active link, and a few times (Public sites, usual access, etc). Add-on has been uninstalled.

Does nothing but put an icon next to my URL bar.

It doesn't seem to do anything. When you click on the icon it takes you to a page where the URLs should be, but no URLs are listed and it doesn't seem to be looking up my bookmarks.

FYI, I don't have any ad blockers installed.

It would be nice if there were instructions. Or at least a start button.

Disappointing. Many of the bookmarks it marked as not working were absolutely fine. Unfortunately, I found out after I'd taken its word for it and deleted about a dozen. It's designed to do just one thing, and it does it badly.

I wish there was a "Not Working" option, rather then give this 1-star. It's not like I had a bad experience exactly, it doesn't seem like it's working with Firefox 57, at least for me. When I click, I just get the page that says "List of expired bookmarks Found unexpired bookmarks." but nothing else.

I downloaded and installed this add-on, but I there are no instructions on how to use it, so it's kind of useless. If the developer sees this, please tell me what to do! I looked at my bookmarks and there is nowhere to start the program, I tried rt-clicking on it, I even searched the web for "how to use 404 bookmarks" and found nothing. I am frustrated! I really need this thing.

First problem was working out how to launch the addon. It adds a jigsaw piece icon to the toolbar. It must say somewhere in the docs but I had to google to find out.
Biggest problem is that it says it lists 'Unexpired bookmarks'. I wondered if this is a typo for expired but many it checked and offered to remove were valid. EG:
https://www.facebook.com (TypeError: NetworkError when attempting to fetch resource.) [Remove]
Amazon.co.uk: Low Prices in Electronics, Books, Sports Equipment & more (TypeError: NetworkError when attempting to fetch resource.) [Remove]

Other links were, indeed, broken.
Others users have found it works but not here, I'm afraid. Pity.
I would file a bug report but the support link takes me to Github and I don't know how to work it.

Download completes but will not install, says it's corrupt.