Examine source code of m a r b l e

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#969696"
    }
  },
  "version": "2.0",
  "name": "m a r b l e",
  "manifest_version": 2,
  "description": "A simple marble texture to add aesthetics to Firefox."
}