Four JavaScript Lines to Defeat New York Times Paywall 15 years ago
You can arbitrarily inject javascript on any page after launch.
Here's how to do it in Safari http://www.youtube.com/watch?v=34D7IR7lNHc
Chrome: View > Developer > Javascript Console
Firefox: Install the firebug extension, which does autocompletion and makes developing much more fun. Not sure if this still works in Firefox 4