Hello, I want to build an extension that shows battery status in one way or another.
I know that Firefox removed this feature long time ago but in original discussions about removing this API it was said to limit it to privileged code. I also confirmed that navigator.getBattery() is still present in modern Firefox and it works.
But I only managed to invoke it in this context. Is it possible to access this API from extensions code?
No, Firefox extensions cannot access navigator.getBattery(). As you stated, this API is only available to privileged code.
In Firefox, “privileged code” generally refers to JavaScript that is part of the browser itself. While extensions have higher privileges than a typical web page, they are not “privileged” in the same sense. For more info on how scripts work internally, check out the project’s Script Security documentation.
The “Web Extension Fallback Document” shown in your screenshot is an implementation detail of how Firefox handles developer tools sessions for extensions. According to this comment, this is necessary because various extension contexts such as the popup or the background are not guaranteed to be active. This fallback document gives devtools something it can always attach to even if other, more specific contexts aren’t available at a given moment in time.
