Share my activity of blogger (but even before I am), I enoooooooooooooormement bookmarks / bookmarks in my Firefox Web browser! I'm unfortunately more of… 2000 bookmarks! So I tell you the hell if I have to check them one by one! Of course, with time, some sites close and disappear, others change the structure of their site / blog, others still migrate and change of name, etc… In short, it is not uncommon that a bookmark will lead to a 404 (page not found error) page! To verify that the bookmarks are still valid, they exist various solutions in the form of software, but personally, being an exclusive user of Firefox, I don't like too much use "external" software to Firefox to access data in Firefox, I use a plugin that integrates with Firefox and dedicated to this. I did not need to retrieve the bookmarks from other browsers, these are empty! And why open 2 software, Firefox and the auditor of bookmarks, if we can open one, Firefox? Unfortunately, Firefox does not natively include the audit of bookmarks function, it includes of course a Manager, but I would say it is the most basic. Fortunately there are plugins to Firefox! Unfortunately (again!) and oddly, there are very few plugins dedicated to this feature is the verification of the bookmarks! I even found one that does its job quite correctly: Bookmarks Checker like any Firefox plugin, simple to install! Click on "Add to Firefox", accept, and restart Firefox. After the reboot, a small icon appears as a yellow star with a V in Green: A c
lick on this icon, and presto, a new window will appear:
you can also change the scan mode by choosing from the drop-down list of "Scan Mode" and choose from the proposal:
entirely in English, but not complicated. So as you can see, it will test all your bookmarks and you list those who are in errors (or double – empty folders, etc.) Depending on the scan mode that you have previously defined) and the scan is done very quickly! For my more than 2000 bookmarks, it does the trick (for the scan in "Bad & Others Errors") in a few minutes! Then he gives you the result as a list with checkbox: on one side, you have the title, and on the other, 
the link: so you have several means of action: open the link, copy the link, put in white list so that the next time it scans over this link, delete the bookmark of the page of results and of course delete the bookmark in the browser! Of course, like any software/plugin of automation, it is more than advise to check if the results are correct or incorrect. On the other hand, damage that one is forced to check a box or to right click and click on 'Open URL' to open the link, a double click would have been so convenient! As well as integration in the pane of the bookmarks of Firefox. It is also available for Chrome: https://chrome.google.com/webstore/detail/bookmark-checker/lnboppjpcdnckcklbmjmdahfkpmgglec
For FF Bookmarks Checker is not available any longer.