Examine source code of Send to Slack

{
  "manifest_version": 2,
  "name": "Send to Slack",
  "description": "Easily send pages, media, and links to an HTTP endpoint (e.g., a Slack channel's WebHook).",
  "version": "4.0",
  "permissions": [
    "contextMenus",
    "storage"
  ],
  "optional_permissions": [
    "http://*/",
    "https://*/"
  ],
  "icons": {
    "16": "icon-16.png",
    "19": "icon-19.png",
    "48": "icon-48.png",
    "64": "icon-64.png",
    "128": "icon-128.png",
    "256": "icon-256.png"
  },
  "options_ui": {
    "page": "options.html",
    "chrome_style": true,
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "utils.js",
      "toslack.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "to-slack-chrome-ext@barneyb.com",
      "strict_min_version": "42.0"
    }
  }
}