Seen in my terminal, after starting current nightly with a mostly-fresh profile, doing a search, and clicking on a link. Not sure of exact STR, but that probably doesn't matter. { WARNING: content window passed to PrivateBrowsingUtils.isWindowPrivate. Use isContentWindowPrivate instead (but only for frame scripts). pbu_isWindowPrivate@resource://gre/modules/PrivateBrowsingUtils.jsm:25:14 injectController@resource://gre/modules/MozSocialAPI.jsm:49:20 WARNING: content window passed to PrivateBrowsingUtils.isWindowPrivate. Use isContentWindowPrivate instead (but only for frame scripts). pbu_isWindowPrivate@resource://gre/modules/PrivateBrowsingUtils.jsm:25:14 injectController@resource://gre/modules/MozSocialAPI.jsm:49:20 WARNING: content window passed to PrivateBrowsingUtils.isWindowPrivate. Use isContentWindowPrivate instead (but only for frame scripts). pbu_isWindowPrivate@resource://gre/modules/PrivateBrowsingUtils.jsm:25:14 injectController@resource://gre/modules/MozSocialAPI.jsm:49:20 WARNING: content window passed to PrivateBrowsingUtils.isWindowPrivate. Use isContentWindowPrivate instead (but only for frame scripts). pbu_isWindowPrivate@resource://gre/modules/PrivateBrowsingUtils.jsm:25:14 injectController@resource://gre/modules/MozSocialAPI.jsm:49:20 WARNING: content window passed to PrivateBrowsingUtils.isWindowPrivate. Use isContentWindowPrivate instead (but only for frame scripts). pbu_isWindowPrivate@resource://gre/modules/PrivateBrowsingUtils.jsm:25:14 injectController@resource://gre/modules/MozSocialAPI.jsm:49:20 } This warning was just recently added in bug 1069059 (and indicates that this SocialAPI code needs tweaking)