Duplication of bookmarks -- an ongoing problem

Duplication of bookmarks is an ongoing problem since there is no notification to the user that a bookmark ‘already exists’ when the user ‘adds’ it.

The problem can be multiplied significantly in an import because of the potentially large number of bookmarks that the user may have in the imported file.

How difficult would it be to add (1) a simple filter that would provide notification of duplicates, and (2) ways for users to eliminate already-existing duplicates, without going ‘one by one’?