fix for #27984, r=alecf, a=rickg. implement GetLastPageVisited. also, for now, don't stuff the url in the history db (or use it for GetLastPageVisited) if it is not http: or https:. There is a bug here, we call AddPage() too often and with url that should not be in the history db. this makes history usuable for beta, and prevents mailnews, about:blank, javascript:, file: and chrome: urls from getting in the history db.

modules/libpref/src/init/all.js

@@ -109,6 +109,8 @@ localDefPref("browser.addressbook_location",    "");
 localDefPref("browser.socksfile_location",      "");
 localDefPref("browser.ldapfile_location",       "");
 
+pref("browser.history.last_page_visited", "");
+
 pref("browser.url_history.URL_1", "");
 pref("browser.url_history.URL_2", "");
 pref("browser.url_history.URL_3", "");