Simple Addon: works with jpm run but not after installing the xpi:

Question

following the Tutorials i made an addon which is working with "jpm run" but not after installing the xpi file. I read the issue197 but thats for "icons". The AddOn is shown correctly both ways.

But the clickEvent only works with "jpm run".

Function of the AddOn: clicking in the frame.html runs the javascript

function FrameClick(){  
        window.parent.postMessage("Frame is clicked","*");  
} 

The index.js should then open a Panel.

My code in index.js:

var data = require("sdk/self").data;
var mypanel = require("sdk/panel").Panel({
  contentURL: data.url("panel.html"),
  contentScriptFile: data.url("panel.js")
});

var { Frame } = require("sdk/ui/frame");
var frame = new Frame({                         
    url: "./frame.html"}
);

var { Toolbar } = require("sdk/ui/toolbar");
var toolbar = Toolbar({ 
  name: "toolbar",
  title: "Toolbar",
  items: [frame]
});

frame.on("message",MessageFromFrame)

function MessageFromFrame(e){
    console.log("MessageFromFrame: "+e);
    mypanel.show({position: {top:10,left:10}});
}

mypanel.on("show", function() {
    mypanel.port.emit("show",ShowFromMyPanel); 
});

function ShowFromMyPanel(e){
    console.log("ShowFromMyPanel: "+e); 
}

The data structure is:

myaddon
 index.js
 package.json
myaddon/data
 frame.html
 frame.js
 panel.html

Any suggestions where to look for the error? Thanks for reading :)