Prototyping

This WebExtension has two main features:

1. Sorting bookmark on creation
2. Importing existing bookmarks

Sorting bookmark on creation

This one is simple, a listener on bookmarks.onCreated that run the sorter.

Importing existing bookmarks

This one is a bit more complex because it implies storing user preferences while preventing unwanted behaviour.
Most users will not want the import to work on all bookmarks, so relying on a whitelist/blacklist duo users will be able to either set bookmark folders to import from or set bookmarks folder not to import from.
Import will be a on-demand feature, accessible from the option page. After looking around existing WebExtensions, PrivacyBadger seems like a nice informational base to code from.