Examine source code of ReFont

{
  "manifest_version": 2,
  "name": "ReFont",
  "version": "1.5resigned1",
  "description": "Change the font of any website to one of your choice!",
  "icons": {
    "64": "Pict64.png",
    "128": "Pict128.png"
  },
  "background": {
    "scripts": [
      "refont.js"
    ]
  },
  "browser_action": {
    "default_title": "ReFont",
    "default_icon": "Pict64.png",
    "default_popup": "browserAction.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "frontend.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "finder.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "<all_urls>",
    "storage",
    "tabs"
  ],
  "options_ui": {
    "page": "mgmt.refont#/general",
    "open_in_tab": true
  },
  "applications": {
    "gecko": {
      "id": "refont@c_ext",
      "strict_min_version": "52.0"
    }
  }
}