Examine source code of Simple Glass FF57

{
  "theme": {
    "images": {
      "theme_frame": "top_N.png"
    },
    "colors": {
      "frame": "#080000",
      "tab_background_text": "#f5f5f5"
    }
  },
  "version": "2.0",
  "name": "Simple Glass FF57",
  "manifest_version": 2,
  "description": "Old theme for the new Firefox.\nThe theme is transparent, if it's supported by the system."
}