Examine source code of Test Drive

{
  "theme": {
    "images": {
      "theme_frame": "HTTYDfirefoxHEADER.jpg"
    },
    "colors": {
      "frame": "#a3f1c5",
      "tab_background_text": "#486563"
    }
  },
  "version": "2.0",
  "name": "Test Drive",
  "manifest_version": 2,
  "description": "A fun, photoshopped image from How to Train Your Dragon."
}