kill ::selection { /* hard to see color */ }

avoid-awesome-selection.user.js

// ==UserScript==
// @name           avoid awesome selection
// @namespace      http://uu59.org/
// @version        1.0.0
// @include        *
// ==/UserScript==

// tested on http://www.vimninjas.com//2012/08/28/vim-for-rubyists-part-1/

function addStyle(css) {
  var id = "avoid-awesome-selection";
  var style = document.querySelector('#' + id);
  if(!style) {
    style = document.createElement('style');
    style.id = id
    style.type = "text/css";
    document.querySelector('head, body').appendChild(style);
  }
  style.appendChild(document.createTextNode(css));
}

// ::selection colors cannot restore default?
// http://stackoverflow.com/questions/8676276/how-can-i-use-css3-selection-without-changing-the-default-color-and-background 
var style = '{'+
  'color: #010101 !important;'+
  'background: rgba(200,200,255, 0.99) !important;'+ // for chrome: http://www.w3.org/TR/selectors/#selection
  'text-shadow: none !important;'+
  'box-shadow: none !important;'+
  '-moz-box-shadow: none !important;'+
'}';

// should not use "," for multiple rules(they are ignored), should dependent each rules
addStyle('*::selection ' + style);
addStyle('*::-moz-selection ' + style);

manifest.json

{
  "manifest_version": 2,
  "name": "avoid awesome selection",
  "version": "1.0.0",
  "description": "get out ::selection { color: #000; background-color: #111; }",
  "icons": 
  {
  },
  "content_scripts": [
    {
      "js": [
        "avoid-awesome-selection.user.js"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ]
}