This quick TamperMonkey script can be installed in much the same way as the "select code" block from this question: How to make `select code` work with google chrome?
TamperMonkey is compatible with "Google Chrome, Opera, Chromium and a lot of their derivates like CoolNovo and Rockmelt."
// @name Makes the top bar "fixed"
// @namespace http://www.example.com/
// @description Makes the top bar "fixed"
// @include http://tex.stackexchange.com/*
// @include https://tex.meta.stackexchange.com/*
var $ = unsafeWindow.jQuery;
$("div.topbar").css('position','fixed'); // Fix the topbar
$("div.topbar").css('z-index','5'); // Move it to the top
$("div#header").css('padding-top','25px'); // Pad the rest of the page
Install the Tampermonkey Web Extension for Chrome: Link to Web Store
This should enable a new button that appears by your URL bar. Use the "Add a new script..." button to, well, add a new script.
Copy and paste the code from above into the window that appears.
Be sure to use the "Save" button (not "Save to Disk" ) to save and enable the script.
Enjoy! The script is enabled by default only on TeX.SE and Meta.TeX.SE, but it would probably be usable on other 2.0 SE sites with appropriate alterations to the