Hi there,
This sounds simple. I can build such plugin in 1h. I would code it in JavaScript using Kango framework, so I would deliver the compiled .crx plugin and the source project which you can change and compile into crx file, if needed.
So on browser button click it will show the plugin popup containing an image with 2 buttons over it, once logs "Hello" to console and the other one updates the image src.
Let me know if I understood well, and if Kango framework works for you.
Regards,
Julijan