How to save a file from js (from tiddlywiki code)

gistfile1.js

function mozillaSaveFile(filePath,content)
{
	if(window.Components) {
		try {
			netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
			var file = Components.classes["@mozilla.org/file/local;1"].createInstance(Components.interfaces.nsILocalFile);
			file.initWithPath(filePath);
			if(!file.exists())
				file.create(0,0664);
			var out = Components.classes["@mozilla.org/network/file-output-stream;1"].createInstance(Components.interfaces.nsIFileOutputStream);
			out.init(file,0x20|0x02,00004,null);
			out.write(content,content.length);
			out.flush();
			out.close();
			return true;
		} catch(ex) {
			return false;
		}
	}
	return null;
}