Showing Source By URL in Firefox

A simple question popped up on IRC today: How to get Firefox to show the source of a webpage given by the URL instead of having to show the page and then selecting "View source". The solution is to use the view-source:-qualifier: view-source: to see the HTML source for Wikipedia’s front page. The solution was presented over at Stuart Langridge’s blog where he also presents a simple bookmarklet for swapping source view on and off in the current window.