Examine source code of sync heatmap

{
  "icons": {
    "48": "icon48x48.png",
    "96": "icon96x96+0.png"
  },
  "browser_action": {
    "browser_style": true,
    "default_title": "sync strava heatmap to google map ",
    "default_popup": "menu.html"
  },
  "description": "sync strava heatmap and google map ",
  "manifest_version": 2,
  "name": "sync heatmap",
  "permissions": [
    "https://www.strava.com/heatmap*",
    "https://www.google.com/maps*",
    "https://craigphicks.github.io/sync_heatmap/*",
    "tabs"
  ],
  "version": "1.2",
  "background": {
    "scripts": [
      "webextension-polyfill-0.4.0.d/browser-polyfill.min.js",
      "background.js"
    ]
  }
}