CheckPlaces checks your bookmarks are current. I tried it thinking I have a couple of hundred bookmarks and CheckPlaces found 1555 bookmarks. I would hate to check them manually.
Download CheckPlaces from addons.mozilla.org/en-US/firefox/addon/checkplaces/. The author is the same person who developed Total Validator. CheckPlaces appears to be developed with the same attention to detail.
Some checks take several seconds while others scream through at several per second. The total check used 8.77 minutes.
Some of my older bookmarks produced valid messages about invalid certificates because certificates do expire and I do not keep them current for test sites.
There were 72 DNS errors, 86 page errors, 11 server errors, 1 missing file, 10
questionable bookmarks, 105 duplicates, and 3 empty folders. Each type of problem is in a separate list for easy checking. I quickly deleted the three empty directories.
questionable bookmarks were mostly ones that require a login. Some of the duplicates were obvious and quickly deleted. Other duplicates had the same link but different descriptions suggesting they were picked up at different times.