[chrismorgan]

Just so you know, the immediately-invoked function expression (IIFE) syntax is unnecessary here. This would do:

  javascript:document.designMode=document.designMode=='on'?'off':'on'

[hyldmo]

Doesn't seem to work in chrome. Clicking it just sends you to a page that says "on"

[croon]

This works for me in Chrome and Firefox, and is a bit shorter than the others (excluding your parent).

javascript:(function () {document.designMode=document.designMode=='on'?'off':'on';})()