Examine source code of The 90s Firefox.

{
  "theme": {
    "images": {
      "theme_frame": "mozillafirefoxpatternbig.PNG"
    },
    "colors": {
      "frame": "#6b6b6b",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "The 90s Firefox.",
  "manifest_version": 2,
  "description": "Very, very, very simple design. But fudge it. It was done on paint."
}