Is it possible to modify the page (e.g., add a DIV to the BODY) from a background script? Things like document.body.appendChild(…); don’t seem to work.
Or do I have to create a content script and send a message from the background script to the content script?
One of my extensions uses that technique of injecting changes from the background script (for keyboard shortcuts) or popup script (for the UI) using executeScript. In case an example could be helpful: