Examine source code of Vintage Tiles

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#808080",
      "tab_background_text": "#122f42"
    }
  },
  "version": "2.0",
  "name": "Vintage Tiles",
  "manifest_version": 2,
  "description": "I cropped the photo of a vintage-style room, the tiles were the main highlight of the interior. Use this theme if you want to bring a homely feel to your Firefox browser."
}