--- a/devtools/client/definitions.js
+++ b/devtools/client/definitions.js
@@ -506,21 +506,20 @@ exports.ToolboxButtons = [
       ScratchpadManager.openScratchpad();
     }
   },
   { id: "command-button-responsive",
     description: l10n("toolbox.buttons.responsive",
                       osString == "Darwin" ? "Cmd+Opt+M" : "Ctrl+Shift+M"),
     isTargetSupported: target => target.isLocalTab,
     onClick(event, toolbox) {
-      let browserWindow = toolbox.win.top;
-      ResponsiveUIManager.handleGcliCommand(browserWindow,
-        browserWindow.gBrowser.selectedTab,
-        "resize toggle",
-        null);
+      let tab = toolbox.target.tab;
+      let browserWindow = tab.ownerDocument.defaultView;
+      ResponsiveUIManager.handleGcliCommand(browserWindow, tab,
+        "resize toggle", null);
     },
     isChecked(toolbox) {
       if (!toolbox.target.tab) {
         return false;
       }
       return ResponsiveUIManager.isActiveForTab(toolbox.target.tab);
     },
     setup(toolbox, onChange) {