firefox - How to get the active tab URL in an e10s add-on -

for toolbar button click, need url address of active tab.

but

window.gbrowser.selectedbrowser.contentdocument 

gets cpow error.

how can url location of active tab url within e10s add-on?

looking around @ objects available, , in source code, looks should uri active tab is:

from current nsiuri:

window.gbrowser.currenturi.spec 

the object window.gbrowser.currenturi returns nsiuri has number of properties uri, including:

[nsiuri].spec //returns string representation of uri.  [nsiuri].asciispec //the uri spec ascii compatible encoding.  [nsiuri].specignoringref //returns string representation of uri without ref                          //  (part after #) portion. 

you can nsiuri current selected tab as:

window.gbrowser.selectedbrowser._documenturi 

from urlbar:
could, of course, pull url out of urlbar:

window.document.getelementbyid('urlbar').value 

finding window:
of above assume have set window appropriately active window. example, doing like:

    //  add/remove "/" comment/un-comment code appropriate add-on type.     /* add-on sdk:     let window = require('sdk/window/utils').getmostrecentbrowserwindow();     //*/     //* overlay , bootstrap (from context/scope):     components.utils.import("resource://gre/modules/services.jsm"); //services     let window=services.wm.getmostrecentwindow("navigator:browser");             //*/