Changes

* Follow [https://developer.mozilla.org/En/Simple_Firefox_build these instructions] to build Firefox for desktop, just so that you can build xpcshell. As an alternative, you can download a "tests" zip from a current build for your platformfrom [ftp://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-mozilla-central/ here], such as ftp://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-mozilla-central/firefox-23.0a1.en-US.linux-i686.tests.zip -- unzip and find xpcshell.