The browser extension HTTPS Everywhere has a conflict with Overclock.net that prevents thread previews from displaying on hover and the subscribe button is made non-responsive. In order to fix these issues open HTTPS Everywhere’s preferences and enter “Yahoo!” into the search box. Right click on “Yahoo! (partial)” and select toggle to disable the filter. If Overclock.net was open while you changed these settings then refresh the page and both features should work normally.