How would one check the status of website saved as bookmarks, without clicking and loading each entry individually? For reference, I use Mozilla Firefox.
This seems to be a pretty good extension for Firefox that does what you want. https://addons.mozilla.org/en-US/firefox/addon/bookmarks-checker/
It adds a small icon between the URL field and the search field in firefox. When you click it you can initiate a scan of all your bookmarks.
Description from addons.mozilla
Bookmarks Checker. Scan favorites for broken or dead links. Delete empty, and duplicate folders. Check bookmarks for broken or dead/broken links. Add bookmarks that you do not want to be scanned to ignore list. Scans for 404 bookmarks, Time-out links or 403 favorites. Scan for duplicate folders. Scan for empty folders. Scan in several threads. Set timeout setting for bookmarks
The Firefox extension 404 Bookmarks has excellent results, and lists both the 404 bookmark and the bookmark with other kinds of errors.
The description reads:
With this extension you can find expired bookmarks and remove them easily. You can find all kinds of broken bookmarks, like pages that return 404 (Page not found) or other HTTP errors.
The category "Other bookmarks" contains all other kinds of HTTP errors, like 403 (Forbidden) or 503 (Service Unavailable), but can also indicate that a DNS lookup for this page failed. You should always make sure that these links are actually broken before deleting them.