Offline first for online content? Whoa buddy, where's this Moon you're asking for?
Seriously though, you need to be realistic when you're asserting your wants for a service or tool. Everyone builds tools to sync bookmarks and save lists now, because that's a feature that users want. It's going to be difficult to find something that is "offline".
Try using a memo app maybe? Lots of password managers have the ability to save links, and would technically be "outside" the browser if you want them to be.