So: pass the URL to FB to decode to canonical value, and return that for further operations (share, copy/paste, etc.).

This would have to be through an extension or an internal browser function.

The canonicalisation request would have to be w/o the initial person's FB identifiers as part of the request (e.g., cookies, etc.). FB might cotton on to immediate re-requests after URL provision, though that would be an interesting approach and yet further signs of expressly violating expressed intent.