How to debug CSS/Javascript hover issues

I often find myself wanting to debug CSS layout issues that involve DOM changes caused by Javascript in reaction to a hover event or different CSS rules applying due to the :hover selector.

Normally, I'd use Firebug to inspect the element that's giving me trouble and see what its CSS properties were, and where those properties come from. However, when hovering is involved, it becomes impossible, because as soon as you move your mouse down to the Firebug panel, the elements you're interested in are no longer hovered, the CSS rules that apply are different, and (in the case of JS hovers) the DOM is changed.

Is there any way I can "freeze" the state of the DOM and application of :hover in order to inspect the DOM as it was during a hover event?

Any other ideas on how to debug this sort of issue are welcome, of course.

You can do this in Firebug but its a little "buggy". If you inspect the element and then click off the the html tab, to the DOM tab for instance, when you go back to the html tab the "style" css tab on the right will have an arrow drop down selector where you can select the :hover state of that element to be active. Sucks to have to switch tabs to get it to show but it works for me.

When inspecting links, Firebug shows the default CSS state, i.e. styles applied to a:link. By default, the :hover and :active styles are not shown. Fortunately, you can change the state of the link by clicking Style and choosing the appropriate option:

Add an onmouseover function handler to the element that is taking the :hover. Inside that function, call console.info(element) on whichever element you'd like to know about.

myHoverElement.onmouseover = function() {
    console.info(document.getElementById("someotherelementofinterest"));
};

When you run this with firebug active, the element will be available to inspect in the firebug console.

In firebug, while in the HTML view, look to the right-side panel and find the "Styles" tab. Click the down arrow and select :hover.