Examine source code of Tentacles

{
  "theme": {
    "images": {
      "theme_frame": "Tentacles-Banner.png"
    },
    "colors": {
      "frame": "#d1d1d1",
      "tab_background_text": "#212121"
    }
  },
  "version": "2.0",
  "name": "Tentacles",
  "manifest_version": 2,
  "description": "Tentacles theme which I've used in one or two other applications (desktop wallpapers etc), thought it would look nice in Firefox.  I made it all in Photoshop CS3.  Hope you like :)"
}