Refresh Your Bookmarks од Robert Rothenberg

This bookmark will show a notification if you visit a bookmarked page and one of the following:
- The page has a canonical url that is different from your bookmarked URL;
- The bookmarked URL redirected to another page or an HTTPS page;
- The server replied with an error code to indicate that the page might be inaccessible;
- The hostname could not be reached;
You can click on the notification, and it will make the recommended changes.