Examine source code of Linux Lite - Default

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#e9e9e9",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Linux Lite - Default",
  "manifest_version": 2,
  "description": "Built to match the default theme in Linux Lite 2.8!  This theme works well with the Firefox shipped with Linux Lite but the tabs may be a bit hard to see on the Windows version of Firefox.  If you want a Linux Lite theme for your Windows version of Firefox, try the dark version instead."
}