Examine source code of FFMurrinaChrome

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#7babe4",
      "tab_background_text": "#000"
    }
  },
  "version": "2.0",
  "name": "FFMurrinaChrome",
  "manifest_version": 2,
  "description": "Since FF has disabled GTK2 support in version 53, I made this theme using the exact color of the \"MurrinaChrome\" theme, in order to have a better integration even with the GTK3 engine."
}