Every time you visit a page which the server reports as permanently moved, this extension will search for bookmarks for to the old page, and update the URL for the new page.
All status codes other than 301 & 308 are ignored. This includes 200, 404, 403, 500, etc.
It's worth noting that HSTS (HTTP Strict Transport Security) upgrades aren't detected by the extension, as these don't generate a request to / response from the server. (They happen client side.)
The extension updates the URL only - no changes are made to tags, folders/directories, title, description, etc.
