Examine source code of MLD2 - Skulls Theme

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#999999"
    }
  },
  "version": "2.0",
  "name": "MLD2 - Skulls Theme",
  "manifest_version": 2,
  "description": "The common art used for MLD2 (Master Levels for Doom 2), now a theme for Firefox!"
}