Examine source code of A11yFocus

{
  "name": "A11yFocus",
  "version": "0.1.1",
  "manifest_version": 2,
  "description": "Quickly debug focus problems when testing a page for accessibility issues.",
  "devtools_page": "src/devtools/devtools.html",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "background": {
    "scripts": [
      "src/bg/background.js"
    ]
  },
  "applications": {
    "gecko": {
      "id": "@a11yfocus",
      "strict_min_version": "55.0"
    }
  },
  "permissions": [
    "tabs",
    "http://*/*",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "all_frames": true,
      "js": [
        "vendor/jquery-3.3.1.js",
        "src/inject/inject.js"
      ]
    }
  ]
}