I understand the conceptual differences between background and content scripts as there are plenty of articles and threads on it, but I’m not sure how these differences look in practice. I’m not sure exactly what makes a script a background script or a content script - it seems to be implicit, but I’m not sure based off what.
For example, in this example: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_second_WebExtension, there is a file called beastify.js in a folder called content_scripts, so I’m guessing that’s a content script. But there is another file called choose_beast.js in a directory called popup, and I’m not sure whether that counts as a background or a content script. I see no differences between beastify.js and choose_beast.js that should tip me off as to what type of file choose_beast.js is. Maybe I am overthinking this.
Which is it, and how can I tell based on the code in the file?