The Bookmark Link Checker Firefox extension will detect updated, redirected and broken links in your bookmarks list by adding icons within the drop-down bookmarks menu.
To evaluate links: You can right click on each bookmark in the drop-down menu or you can use the "Check" button added in the Bookmarks Manager's toolbar. View->Show Columns->BLC to show icons in both the Bookmarks Manager window as well as the drop-down menu.
Icon descriptions can be located in the options menu of the add-on.