Changes

| valign="top" |[https://bugzilla.mozilla.org/show_bug.cgi?id=335963 Improve link activation APIs] to consolidate link activation code, fix bugs caused by inconsistencies and allow single-window and tabbed-only browsing and open-in-new-window / open-in-new-tab context menu options that really work, even for javascript: URLs and onclick handlers. And then get at least a significant start on the front-end changes needed to use those APIs. See [https://bugzilla.mozilla.org/show_bug.cgi?id=335963 bug] for more details.