> So I did more tests and here are some comments and questions:
Ah, and something else:
- In scripts/background/background.js it seems like you are activating
  the extension on 
https://tails.boum.org/install/download_2/ but:
  - This URL is bound to change once we release the extension.
  - The extension should be activated on several pages, for example:
    - https://tails.boum.org/install/win/usb
    - https://tails.boum.org/install/debian/usb
  In Giorgio's code we were using a div id #download-and-verify instead,
  so that the extension could be activated on multiple pages. Could we
  go back to doing something like this instead? If that works for you,
  I'll add a div id in my HTML code.