STR: -1. apply patch from bug 1006989 so that selectedNode can be null in some cases, and selectedNodes can be an empty array. 0. Open browser toolbox 1. Find controller.js (in places code) 2. Set a breakpoint on the first line of openSelectionInTabs 3. Right click an empty part of your bookmarks toolbar (make it visible if it isn't already) 4. When the breakpoint gets hit: 4a. expand |this| 4b. expand |this._view| 4c. (optional) set a watch for |this._view.selectedNode| 4d. (optional) set a watch for |this._view.selectedNodes| AR: |this._view| doesn't list |selectedNode| or |selectedNodes| as a property, even though the watches clearly show they are set to |null| and || respectively. ER: see these properties in the list for |this._view| .
With the new debugger front end I can see both "null" and "" values in the object inspector. I'm afraid that won't help you, though, because the browser debugger is still using the old front end.