Examine source code of SelectCalc

{
  "manifest_version": 2,
  "name": "SelectCalc",
  "version": "2.2resigned1",
  "description": "Calculates highlighted expressions in input fields and text areas.",
  "homepage_url": "https://code.s.zeid.me/selectcalc",
  "applications": {
    "gecko": {
      "id": "selectcalc@ns.bnay.me",
      "strict_min_version": "63.0"
    }
  },
  "background": {
    "scripts": [
      "expr-eval.min.js",
      "decimal.min.js",
      "decimal-parser.js",
      "calculator.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "permissions": [
    "contextMenus",
    "tabs",
    "<all_urls>"
  ],
  "commands": {
    "evaluate-selection": {
      "suggested_key": {
        "default": "Ctrl+Alt+E"
      }
    }
  }
}