Automate Page Load Performance Testing with Firebug and Selenium
Your best bet would probably be to use Browsermob proxy in conjunction with Selenium. It will allow you to run Firefox without plugins, and to output the har file. The project has the creator of Selenium on board, and some other well known figures. The Github Project has a sample which shows how to create the Har file, from there you could write your own code to process it and ensure your performance metrics are met, or that your included javascript / css was located, write it to disc, etc...