zoom.user.js

// ==UserScript==
// @name          autoPage
// @description   page zoom
// @include       *
// @exclude       
// ==/UserScript==
autoPage();
function autoPage(){
        var zoomLevel=150; //default zoom level, 150 means zoom level is %150.
        zoom(zoomLevel);
}
function zoom(level)
{
        var i = parseInt(document.body.style.zoom);
        if (isNaN(i)) i=100;
        newZoom= i * level / 100;
        document.body.style.zoom=newZoom+'%';
}