Currently every bookmark registers for URL load notifications, so on every URL load, the notification manage will fire off notifications to potentially hundreds of bookmarks. This is done to set last-visit dates (which we don't really use anywhere anyway). This sucks. If we really want to maintain last-visit, we should maintain a single observer of URL loads that has a map from URL to bookmark items.
isn't it also used for computing the top10 list visit counts?
Fixed now; the bookmarks manager does the load listening, and forwards out to the relevant bookmarks.