This previously checked whether the first octet was non-zero, treating
most IPv4 addresses (e.g. 183.189.143.11) as potentially trustworthy.
Match the first octet against 0x7f so only 127.0.0.0/8 is trusted.
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.