Examine source code of Upload progress

{
  "description": "This addon show upload progress",
  "manifest_version": 2,
  "name": "Upload progress",
  "version": "1.0",
  "homepage_url": "https://4xmen.ir",
  "icons": {
    "48": "icons/border-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "upload.js"
      ]
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d6b31f74-0918-496a-be59-aea206d565f5}"
    }
  }
}