Ember Simple Auth on Firefox: authentication throws Error

I am extending Ember Simple Auth's base authentication class to allow authentication with Google. So far, it works on Safari 8 and Chrome 41 (both on Yosemite) with no errors. However, on Firefox 35, it throws an Error that does not occur on the other browsers. Here is my Google authenticator class:

App.GoogleAuthenticator = SimpleAuth.Authenticators.Base.extend({
    // constants for Google API
    GAPI_CLIENT_ID: '140682596441-gqjefmvll1rishgo9235sjrlkle4gvqp.apps.googleusercontent.com',
    GAPI_SCOPE: ['email'],
    GAPI_TOKEN_VERIFICATION_ENDPOINT: 'http://ift.tt/1fx4kzd',

    // method for scheduleing a single token refresh
    // time in milliseconds
    scheduleSingleTokenRefresh: function(time) {
        var self = this;
        return new Ember.RSVP.Promise(function(resolve, reject) {
            Ember.run.later(self, function() {
                gapi.auth.authorize({
                    client_id: self.GAPI_CLIENT_ID,
                    scope: self.GAPI_SCOPE,
                    immediate: true
                }, function(data) {
                    if (data && !data.error) {
                        resolve(data);
                    } else {
                        reject((data || {}).error);
                    }
                });
            }, time);
        });
    },
    // WIP: recursive method that reschedules another token refresh after the previous scheduled one was fulfilled
    // usage: scheduleTokenRefreshes(time until token should refresh for the first time, time between subsequent refreshes)
    // usage: scheduleTokenRefreshes(time between refreshes)
    scheduleTokenRefreshes: function(time1, time2) {
        var self = this;
        // if there is a time2, schedule a single refresh, wait for it to be fulfilled, then call myself to schedule again
        if (!Ember.isEmpty(time2)) {
            self.scheduleSingleTokenRefresh(time1)
            .then(function() {
                self.scheduleTokenRefreshes(time2);
            });
        // if there isn't a time2, simply schedule a single refresh, then call myself to schedule again
        } else {
            self.scheduleSingleTokenRefresh(time1)
            .then(function() {
                self.scheduleTokenRefreshes(time1);
            });
        }
    },

    // method that restores the session on reload
    restore: function(data) {
        var self = this;
        return new Ember.RSVP.Promise(function(resolve, reject) {
            console.log(data);
            if (Ember.isEmpty(data.access_token)) {
                reject();
                return;
            }
            // schedule a refresh 15 minutes before it expires or immediately if it expires in < 15
            var timeNow = Math.floor(Date.now() / 1000);
            var expiresAt = +data.expires_at;
            var timeDifference = expiresAt - timeNow;
            var schedulingDelay = Math.floor(timeDifference - 15 * 60);
            schedulingDelay = schedulingDelay < 0 ? 0 : schedulingDelay;
            self.scheduleTokenRefreshes(schedulingDelay * 1000, 45 * 60);
            resolve(data);
        });
    },
    // method that authenticates
    authenticate: function() {
        var self = this;
        return new Ember.RSVP.Promise(function(resolve, reject) {
            gapi.auth.authorize({
                client_id: self.GAPI_CLIENT_ID,
                scope: self.GAPI_SCOPE
            }, function(data) {
                if (data && !data.error) {
                    // schedule a refresh in 45 minutes
                    var schedulingDelay = 45 * 60;
                    self.scheduleTokenRefreshes(schedulingDelay * 1000);
                    resolve(data);
                } else {
                    reject((data || {}).error);
                }
            });
        });
    },
    // method that logs the user out and revokes the token
    invalidate: function(data) {
        var self = this;
        return new Ember.RSVP.Promise(function(resolve, reject) {
            // send a GET request to revoke the token
            Ember.$.ajax({
                type: 'GET',
                url: 'http://ift.tt/1j4gPSy' + self.get('session.access_token'),
                contentType: 'application/json',
                dataType: 'jsonp'
            })
            .done(function(successData) {
                resolve(successData);
            })
            .fail(function(error) {
                reject(error);
            });
        });
    }
});

When the popup window closes after a successful login on Google's end, this error appears on Firefox's console:

Error: Assertion Failed: Error: Permission denied to access property 'toJSON' ember.js:13749
"__exports__.default<.persist@http://ift.tt/1vbYJsE
__exports__.default<.updateStore@http://ift.tt/1JQxoPB
__exports__.default<.setup@http://ift.tt/1vbYMos
__exports__.default<.authenticate/</<@http://ift.tt/1JQxoPG
tryCatch@http://ift.tt/1vbYMEL
invokeCallback@http://ift.tt/1JQxoPP
publish@http://ift.tt/1JQxoPR
@http://ift.tt/1JQxp65
Queue.prototype.invoke@http://ift.tt/1vbYJsM
Queue.prototype.flush@http://ift.tt/1JQxmHI
DeferredActionQueues.prototype.flush@http://ift.tt/1vbYJJ2
Backburner.prototype.end@http://ift.tt/1vbYMEZ
createAutorun/backburner._autorun<@http://ift.tt/1JQxmY0
" ember.js:29488

The most confounding thing is that this only appears on Firefox. Is it a bug in Ember Simple Auth or Ember? How do I fix it?