var file = Components.classes['@mozilla.org/file/local;1'].getService(Components.interfaces.nsILocalFile);
var process = Components.classes["@mozilla.org/process/util;1"].createInstance(Components.interfaces.nsIProcess);
file.initWithPath(C:\\Program Files (x86)\\Nightly\\firefox.exe);
process.init(file);
var args = ["-p", "nightly", "-no-remote"];
process.run(false, args, args.length);