dct.uc.js

// ==UserScript==
// @name    domain color tab
// @desc    Color-codes each tab by the domain of its content.
// @include main
// @compat  Fx39+
// @author  satyr
// @license X
// ==/UserScript==
{
let c = '8ace'
  , palette = [for (r of c) for (g of c) for (b of c) '#'+r+g+b]
  , {require} =
      Cu.import('resource://devtools/shared/Loader.jsm', null).devtools

require('sdk/tabs').on('ready', tab => {
  var [, domain] = /^https?:\/+([^\/]+)/.exec(tab.url) || []
  if (!domain) return
  require('sdk/view/core').viewFor(tab).style.backgroundColor = palette[
    Array.reduce(
      domain, (s, c) => s + c.charCodeAt(), new Date().getDate()
    ) % palette.length
  ]
})
}