Bookmark Branch Porter

It should be part of Firefox, a feature to export and import bookmark branches. This extension fills that gap. Unfortunately, it breaks some times, without any warning, so we could try to fix it. Another problem is that it cannot export/import metadata (tags, dates etc.), and although that's a Firefox's internal problem, it does make the extension a lot less useful than it should be. In practice, it works just like copying and pasting bookmarks from the bookmark library (from a temporary profile), except that it can copy folders, too.