Bug 841711 - httpd.js extension in DEBUG=1 profiles is broken in current nightly r=fabrice

* Load dbg-client.jsm from the correct URI in new Firefox
* bumped up the version
Bug 843780 - Fix SMS mockup for desktop testing

This script was created to facilitate development on desktops using with
FireFox. It has broken since being implemented. This commit restores the
intended functionality.