Examine source code of Happy Flowers...

{
  "theme": {
    "images": {
      "theme_frame": "HappyFlowers_header_byLisa.jpg"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Happy Flowers...",
  "manifest_version": 2,
  "description": "Bright cheerful yellow and orange hand drawn flowers beautify your Firefox browser, floral, Summer colors\n\nchild friendly persona\n\nPersonas by LisaAtTheBeach"
}