How to get document.popupNode in Firefox Electrolysis windows

Question

I am trying to write an add-on for Firefox Electrolysis. When I open an e10s window and right click on a page element, document.popupNode is not available for e10s window.

var WindowListener = {
    setupBrowserUI: function(window) {
        //
    },
    tearDownBrowserUI: function(window) {
    },
    // nsIWindowMediatorListener functions
    onOpenWindow: function(xulWindow) {
        var domWindow = xulWindow.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
                                 .getInterface(Components.interfaces.nsIDOMWindow);
        // Wait for it to finish loading
        domWindow.addEventListener("load", function listener() {
            domWindow.removeEventListener("load", listener, false);
            // If this is a browser window then setup its UI      
            if (domWindow.document.documentElement.getAttribute("windowtype")=="navigator:browser") {

                domWindow.document.getElementById('contentAreaContextMenu').addEventListener("popupshowing", function(event){

                    let document=event.currentTarget.ownerDocument;
                    let prompts = Components.classes["@mozilla.org/embedcomp/prompt-service;1"].getService(Components.interfaces.nsIPromptService);
                    prompts.alert(null, "Test", document.popupNode);                    

                }, false);

            }

        }, false);
    },
    onCloseWindow: function(xulWindow) {
    },
    onWindowTitleChange: function(xulWindow, newTitle) {
    }
};

let wm = Components.classes["@mozilla.org/appshell/window-mediator;1"].
       getService(Components.interfaces.nsIWindowMediator);
// Wait for any new browser windows to open
wm.addListener(WindowListener);

You can use test code in Scratchpad. After running test code, open a new normal Firefox window and right click inside a web page. Prompt alert appears for the document.popupNode.

But if a new e10s Firefox window is opened and right clicked, it does not show anything.

How can I get the document.popupNode in e10s windows?

Answer 1

There is no document.popupNode because the XUL document didn't pop anything up at a node. Instead it received a message from the child process that told it to display the menu at certain screen coordinates.

Instead, use gContextMenu.target, which is populated from gContextMenuContentData.event.target.

gContextMenu.target is available all browser windows, while gContextMenuContentData.event.target is only available in e10s windows.

Of course, gContextMenu is only valid when a popup is about to show or showing.