The free utility AM-Deadlink can find dead links and duplicates in your list of browser bookmarks.
I run it on my machine every couple of months, to clean things up and save me from wasting time in following dead links. You can download the utility here: AM-Deadlink
It’s easy to install and use, and takes only a couple of minutes to check my 1600 bookmarks. Then I sort the list by error number, and delete any 404 pages.