Product Sans It

You can try Product Sans everywhere.

The following javascript function accomplishes the css injection when initialized:

javascript: (function () {
    var fileref = document.createElement('link');
    fileref.setAttribute('rel', 'stylesheet');
    fileref.setAttribute('type', 'text/css');
    fileref.setAttribute('href', 'http://weiweihuanghuang.github.io/productsansit/productsansit.css');
    document.getElementsByTagName('head')[0].appendChild(fileref);
})();

Just drag this bookmarklet below and drop it to your browser bookmarks toolbar. Every time you click it now, the current website in your browser will change (not working on most SSL-encrypted websites, though).