RTCPeerConnection media stream working in firefox

Trying to keep the problem as simple as possible, I am creating a media stream in a chrome extension like so:

var pc = new RTCPeerConnection(null);
chrome.desktopCapture.chooseDesktopMedia(['screen', 'window'], null, function(streamId) {
    var constraints = {
        audio: false,
        video: {
            mandatory: {
                chromeMediaSource: 'desktop',
                chromeMediaSourceId: streamId
            }
        }
    },
    success = function(stream) {
        pc.addStream(stream);
        pc.createOffer(function(offer) {
            pc.setLocalDescription(offer, function() {
                send('make_offer', name, offer);
            }, printError);
        }, printError);
    };
    getUserMedia(constraints, success, printError);
});

For now, my offer is received by a peer visiting a page in a browser. That looks more or less like this (m is a message object with the offer):

var pc = new RTCPeerConnection(null);
pc.onaddstream = function(e) {
    var video = document.getElementById('video');
    video.src = URL.createObjectURL(e.stream);
};
pc.setRemoteDescription(new RTCSessionDescription(m.value), function() {
    pc.createAnswer(function(answer) {
        pc.setLocalDescription(answer, function() {
            send('make_answer', m.from, answer);
        }, printError);
    }, printError);
}, printError);

I have done this, both with and without ice servers, which look like this when I use them:

var iceServers = {
    iceServers: [
        {url: 'stun:stun.l.google.com:19302'}
    ]
};

Right now, the peer receives and displays the stream perfectly in Firefox. No problem at all. But it's not working in Chrome. Here is some selected data from chrome://webrtc-internals: connection to firefox:

"ssrc_3309930214_send-transportId": {
 "startTime": "2014-09-30T01:41:11.525Z",
 "endTime": "2014-09-30T01:41:21.606Z",
 "values": "[\"Channel-video-1\",\"Channel-video-1\",\"Channel-video-1\"]"
},
"ssrc_3309930214_send-packetsLost": {
 "startTime": "2014-09-30T01:41:11.525Z",
 "endTime": "2014-09-30T01:41:21.606Z",
 "values": "[0,0,0,0,0,0,0]"
},

connection to chrome:

"ssrc_1684026093_send-transportId": {
 "startTime": "2014-09-30T01:41:57.310Z",
 "endTime": "2014-09-30T01:42:00.313Z",
 "values": "[\"Channel-audio-1\",\"Channel-audio-1\",\"Channel-audio-1\",\"Channel-audio-1\"]"
},
"ssrc_1684026093_send-packetsLost": {
 "startTime": "2014-09-30T01:41:57.310Z",
 "endTime": "2014-09-30T01:42:00.313Z",
 "values": "[-1,-1,-1,-1]"  // what is causing this??
},

Those seem important, but I'm not sure exactly of the implications. I have more data, but I'm not sure exactly what is important. The main idea, is that data goes out to firefox, but not to chrome, though no exceptions occur that I can see. The one further suspicious piece of data happens if I load the peer page in Chrome Canary (latest):

Failed to load resource: net::ERR_CACHE_MISS

This is a console error, and I don't know where it comes from. It occurs after the answer is sent from the peer back to the host (chrome extension).

Signaling done over wss://, test peer is hosted at https:// I'm not sure where to go from here.

Update: Based on answer and comment, I added a handler for onicecandidate:

pc.onicecandidate = function(e) {
    console.log('This is the ice candidate.');
    console.log(e);
    if(!e.candidate) return console.warn('no candidate!');
    send('got_ice_candidate', name, e.candidate);
};

I also set up an equivalent peer connection from browser to browser using video:

var constraints = {
    audio: false,
    video: true
};
getUserMedia(constraints, success, printError);

This works fine, both from Firefox to Chrome and vise-versa, so the issue may be chrome-extension-specific... There is a difference in how ice gathering occurs between the successful case and the extension case:

Between browsers, there is no ice at all. There is one event, and e.candidate is null.
From extension to browser, there are lots of onicecandidate events. They are not all in agreement. So perhaps the chrome extension is confusing the STUN server? I don't know.

Thanks for your answers, would love any more insight that you have.

can you please add handling ice candidates on both sides ?

pc.onicecandidate = function(e){ send('ice_candidate', e.target) }

And on the other side on receiving this 'message' do

pc.addIceCandidate(new RTCIceCandidate(message));

Chrome sends ice candidates even after offer/answer have been exchanged which firefox does not seem to do.