Assume that I\'ve fired up Firefox with Firebug enabled on a random site (say slashdot.org). After loading the site I start editing the page using the Firebug > HTM
When you're in the HTML section of firebug, there's an "Edit" button on the bar just below firebug's main toolbar. Clicking this button gives you a plain text view of the HTML (with any edits you've made) that you can copy to a text editor.