Examine source code of InstaCalc

{
  "manifest_version": 2,
  "name": "InstaCalc",
  "version": "1.0",
  "description": "WebExtension for instantly calculating expressions on a webpage",
  "homepage_url": "https://github.com/matrizx/instacalc",
  "icons": {
    "128": "logo.png"
  },
  "permissions": [],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "dist/ext.js"
      ]
    }
  ]
}