Improve an awkward initialization behavior in Javelin in Firefox
Summary: See comment; see IRC. This didn't cause anything bad, but ended up with document.body.id == "null" in Firefox, which is a bit weird.
Test Plan: Loaded page, put document.body.null into the console, got consistent results.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D7288