If you have an element currently selected in your "Elements" tab, you can use the reference $0 to call it within your code. For example, to see the elements' contents you would type $0.innerHTML.

In Firebug and Opera, you can select the previous element you had highlighted using $1.

In Chrome and Safari, you can select further previous elements you have highlighted using $1 - $4.

In Firebug, you can select further previous elements you have highlighted using $n(2) - $n(5).