// ==UserScript==
// @name           script
// @include        *
// @run-at document-start
// ==/UserScript==

// Add style rules while page is loading (to prevent jumping)
function addStyleRules(){

    // Check if stylesheets exist yet, if not try again in a bit
    if( !document.styleSheets[0] ) return setTimeout( addStyleRules,1 );

    var ss = document.styleSheets[0];

    // Add style rules
    if(ss.addRule)
        ss.addRule( '*','background-color:black',0);
    else
        ss.insertRule('*{background-color:black}',0);

    //debug
    console.log( 'page loading', ss, new Date().getTime() );
}
addStyleRules();

// Page has finished loading
document.addEventListener('DOMContentLoaded',function(e){

    // Get stylesheet object
    var ss = document.styleSheets[0];

    //debug
    console.log('page loaded', ss, new Date().getTime() );
});