Uses a Mutation Observer to detect when VWO injects it's anti-flicker styles into the page and them removes them - handy for WPT

kill-vwo-anti-flicker-styles.js

callback = function(mutationsList, headObserver) {

    // Use traditional 'for loops' for IE 11
    for(mutation of mutationsList) {

        for(node of mutation.addedNodes) {
            if(node.nodeName === 'STYLE' && node.id === '_vis_opt_path_hides') {
                node.parentNode.removeChild(node);
                performance.mark('vwo-hide-start');
            }
        }
                       
    }
};

headObserver = new MutationObserver(callback);

headNode = document.getElementsByTagName('head')[0];
headObserver.observe(headNode, { childList: true });