Offering usability for Users without Mouse is one of the biggest and most important Steps when building accessible Websites. While testing for Keyboard Accessibility you might find yourself very often in Situations like "Where is my Cursor?" or "What Element has the Focus right now?". Especially when Elements get moved offscreen things might end up confusing.
A Script, I've been using for a while to solve situations like this, I have now converted into a handy Bookmarklet.
LogFocus works in all Browsers that offer a Console. In Firefox you need Firebug. In Safari/WebKit you need to activate the "develop" Menue. For Internet Explorer I recommend using Companion.JS. In Opera the build in Console in Dragonfly is used.
To install the Bookmarklet simply drag the following Link into your Bookmarks.
From there you can run it on every Page by simply clicking on it.