Implement bookmark import/export in about:bookmarks using Netscape
bookmark HTML in JavaScript.
Import parsed items into BookmarkStore under an "Imported Bookmarks"
folder, and treat internal WebUI about: pages as potentially
trustworthy so SecureContext APIs are available there.
This page renders the bookmarks as a tree and hook context menu events
up to the UI's bookmarks bar context menus to allow editing bookmarks.
Users can also drag-and-drop bookmark items around.