Specify dummy loading principal for setAndFetchFaviconForPage()

Since Firefox 50.0a1:
Warning: ‘nsFaviconService::setAndFetchFaviconForPage()’ deprecated, please use ‘nsFaviconService::setAndFetchFaviconForPage(..., [optional aLoadingPrincipal])’
See https://hg.mozilla.org/mozilla-central/rev/e28c4c1378ac

bootstrap.js

@@ -3500,7 +3500,9 @@ var privateTab = {
 					bookmarkURI,
 					Services.io.newURI(icon, null, null),
 					false /*aForceReload*/,
-					faviconService.FAVICON_LOAD_PRIVATE
+					faviconService.FAVICON_LOAD_PRIVATE,
+					null /*nsIFaviconDataCallback aCallback*/,
+					null /*nsIPrincipal aLoadingPrincipal*/
 				);
 			}, 0);
 		}