I am creating a Firefox extension with React.js and want to inject a text into the active website. The permissions, content_script and background script are set in manifest.json but the problem is I do not understand the concept how it should work. So far I tried to add content script but that runs a script at page load and thats it. The background does not seem to interact with the page.

I need a script that listen for an event, when I click on a button in the extension popup, it should send the text from the React app to update the site. Basically like a password manager when you injecting the password into the form field.

Can someone tell me the concept as I do not get what case relevant to my problem after checking in and out the web extension documentation?