3:51.85 INFO Console message: [JavaScript Error: "NotSupportedError: Operation is not supported"]
sendToChildren@chrome://global/content/elements/browser-custom-element.js:2140:24
sendMessageToActor@chrome://global/content/elements/browser-custom-element.js:2151:21
_sendMessage@resource://gre/modules/RemoteWebNavigation.jsm:161:21
stop@resource://gre/modules/RemoteWebNavigation.jsm:123:10
stop@chrome://global/content/elements/browser-custom-element.js:978:26
stop@chrome://browser/content/tabbrowser.js:466:35
Tester_waitForWindowsState@chrome://mochikit/content/browser-test.js:440:16
nextTest@chrome://mochikit/content/browser-test.js:828:10
async*testScope/test_finish/<@chrome://mochikit/content/browser-test.js:1451:25
run@chrome://mochikit/content/browser-test.js:1366:9

 3:51.86 GECKO(15003) JavaScript error: resource://specialpowers/SpecialPowersParent.jsm, line 634: TypeError: this.manager.rootFrameLoader is null
 3:51.86 GECKO(15003) JavaScript error: , line 0: NS_ERROR_UNEXPECTED:
 3:51.87 INFO Console message: [JavaScript Error: "TypeError: this.manager.rootFrameLoader is null" {file: "resource://specialpowers/SpecialPowersParent.jsm" line: 634}]
 3:51.87 INFO Console message: [JavaScript Error: "NS_ERROR_UNEXPECTED: "]