Examine source code of LibrifyJS: sumofus.org

{
  "manifest_version": 2,
  "name": "LibrifyJS: sumofus.org",
  "version": "0.1.2",
  "description": "Allows to sign petitions on sumofus.org with GNU LibreJS running",
  "content_scripts": [
    {
      "matches": [
        "*://www.sumofus.org/"
      ],
      "js": [
        "home.js"
      ]
    },
    {
      "matches": [
        "*://www.sumofus.org/campaigns/"
      ],
      "js": [
        "campaigns.js"
      ]
    },
    {
      "matches": [
        "*://actions.sumofus.org/a/*"
      ],
      "js": [
        "campaign.js"
      ]
    }
  ],
  "permissions": [
    "*://actions.sumofus.org/api/*",
    "webRequest"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{50986b74-eb3b-484c-86ee-f49146b4a07d}"
    }
  }
}