I think this something like ads. Is that correct?. When user click will redirect to products/goods page. Here in page buy/sell goods will taking place with BTC. It seems disturb user to browse with chrome or firefox. Nevertheless it's good idea to implement addon plugins via browser.
Good luck on your project.
The plugin will be used by people who need to buy smth. on the internet with bitcoins but don't have crypto at the current moment. Addon will highlight the bitcoin address of the online store. If you point, it will ask if you would like to buy X bitcoins and send them to the above mentioned address. Then you will be forwarded to a payment page, enter card details and since the payment is completed, bitcoin are sent to online store.