In their tireless march to make every piece of premium software obsolete with free open source, HTML5 applications, Mozilla, alongside Google, has been been at the forefront of this endeavor. While some of the past examples have been really cool like WebRTC, the latest demo has a more practical purpose.
Here's a video demo of the application if you need more of a visual element for learning. Hellmann says that he envisions adding touch support and turning this into a bookmark tool. What other uses can you see for click highlighting? Let us know in the comments.