If you're looking to adjust the firewall adjuster on your Mustang, there are a few things you'll need to keep in mind. First, you'll need to locate the adjustment screws on the back of the firewall. Next, you'll want to loosen the screws so that you can move the firewall around. Once you've got it in the desired position, be sure to tighten the screws back down. And that's all there is to it!