Q:

How to match Firefox's about page in extension manifest?

I would like to match Firefox's about page like so:
"content_scripts": [
  {
    "matches": ["about:debugging"],
    "js": ["import.js"]
  }
]

The script doesn't run. If I try other matches it works properly on "normal" websites.

A:

If I'm not mistaken in Chrome, Firefox, Microsoft, Opera, and Vivaldi these are the things you aren't allowed to modify because they go against extension policies. Meaning, You can't do this, sorry.
about-scheme
chrome-extension-scheme
chrome-scheme
edge-extension-scheme
edge-scheme
moz-extension-scheme
ms-browser-extension-scheme
opera-scheme
vivaldi-scheme
wyciwyg-scheme
(In bold are the ones that will effect Firefox)

