Let me give you a concrete example: you've moved from X to /dev/null
You have 100 bookmarks on X. What will happen with them? Are you going back to X to check them?
Bookmarks are bigger than apps.
I'm now more convinced that bookmarks shouldn't be tied to one platform. Think about it: bookmarks are things you want to remember long-term; they shouldn't be confined to a single website.
My advice? Use a proper bookmarking app or browser extension. Own your bookmarks yourself…