Examine source code of Tab Counter Icon

{
  "manifest_version": 2,
  "name": "__MSG_extName__",
  "version": "0.2resigned1",
  "description": "__MSG_extDesc__",
  "default_locale": "en",
  "homepage_url": "https://addons.mozilla.org/firefox/addon/tab-counter-icon/",
  "icons": {
    "48": "icons/icon.svg"
  },
  "applications": {
    "gecko": {
      "id": "tab-counter-icon@magicp.jp",
      "strict_min_version": "51.0"
    }
  },
  "author": "magicp",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": false,
    "default_icon": "icons/loading.svg",
    "default_title": "__MSG_extTitle__"
  }
}