User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0 Build ID: 20180115221039 Steps to reproduce: Message Browser console start: TypeError: this._prefs is undefined[Learn More] urlbarBindings.xml:146:9 urlbar_XBL_Destructor chrome://browser/content/urlbarBindings.xml:146:9 insertWidgetBefore resource:///modules/CustomizableUI.jsm:1290:5 buildArea resource:///modules/CustomizableUI.jsm:848:9 registerToolbarNode resource:///modules/CustomizableUI.jsm:765:9 registerToolbarNode resource:///modules/CustomizableUI.jsm:3176:5 toolbar_XBL_Constructor Actual results: Browser console start warnings: TypeError: this._prefs is undefined[Learn More] urlbarBindings.xml:146:9 urlbar_XBL_Destructor chrome://browser/content/urlbarBindings.xml:146:9 insertWidgetBefore resource:///modules/CustomizableUI.jsm:1290:5 buildArea resource:///modules/CustomizableUI.jsm:848:9 registerToolbarNode resource:///modules/CustomizableUI.jsm:765:9 registerToolbarNode resource:///modules/CustomizableUI.jsm:3176:5 toolbar_XBL_Constructor Expected results: Just reporting. Maybe help to solve other problem. Thanks.

Hmm, it's like the destructor runs before the constructor, or runs twice, that doesn't sound sane. I don't think this has any consequences, so I don't think it's a priority, but it may be pointing out a more general problem. Ideas on how this may happen are welcome