Angular has a check for Chrome Packaged Apps in its `$sniffer` service
which changes the behavior of the $location service and in the Firefox
extension, triggers a redirect from `/client/app.html` to
`/#client/app.html` on startup, breaking the sidebar app.

This commit works around the problem by adding a fake
`window.chrome.app` object to convince Angular that the Firefox
extension is not a Chrome Packaged App.

Issue reported upstream at https://github.com/angular/angular.js/issues/16068