I've used it several months now, and I can say it works very well. You get a list of expired bookmarks, with the reason (404, 501,...), and checking or removing a bookmark is just one click away. Before a recent update, if you had a lot of bookmarks it opened too many connections after a while, making some links appear as they were down, while they were actually working. But now I can't find any problem ! So thanks for this great, useful extension :-)

Very good tool for the bookmarks.
The icon is standard and not consistent with the use of extension, please choice an other like a folder or a letter B or something like that.
In addition is very similar to an other extension "Simple Add-on Manager" at https://addons.mozilla.org/en-US/firefox/addon/simple-add-on-manager/?src=api.
Better if black like the official Firefox toolbar icons.
Thanks.

Great-worked well & Fast! Would be great if there were an option to delete all 404's with one click.

(Needs some design though)

I've used a couple of other dead bookmark finders and 404 has found ones that the others did not.

I do have to note that I've been on the I'net for 20+ years and have migrated my book marks from Prodigy to Netscape to FF.

404 is the best dead bookmark finder I've used. Yes, it is not perfect. But then, who or what is.