Hey Robert,
I hope you're doing well. I came across your project description and I believe I can help you with it.
I understand that you are looking for an app or plugin for Firefox that will allow you to download audio from a specific website, in this case, emastered.com. You mentioned that there is a "play" button on the website which allows you to listen to the audio, but downloading it requires a subscription fee.
I have experience in PHP, JavaScript, and mobile app development for both iPhone and Android platforms. With my expertise, I can create a solution that will bypass the subscription requirement and enable you to download the audio tracks directly from the website.
I assure you that I will only request payment once you are fully satisfied with the work I deliver. Your satisfaction is my top priority.
If you are interested in discussing this project further or have any additional requirements, please feel free to initiate the chat. I am looking forward to working with you.
Best regards,
Amir