Hi there.
Could you elaborate more on what exact popup you want to manipulate? Can you send me the URL to it so I can see what is requested? I have this in mind: when the popup is opened, you click on the extension button and it will auto-populate and send it as you have requested. If this method works for you, then I can build it.
I would build it for Chrome and Firefox for the price of one.
Also, when do you plan to start this project and when is the deadline, if there is one?
Anyways, feel free to hit me up so we can talk more about this. I am very responsive. All the best