Pointer Lock API means more input for your mouse.

TL;DR: FPS mouse input soon to be natively supported in Chrome browser.

Scheduled for release with Chrome 18, comes the much over-due, [plugin/Java-applet/NaCl]-free, ability to make games for the web with FPS style (or custom) mouse input.

Firefox has an event intercept hack to allow control of the mouse pointer. Up till now, that has been the only plugin-free way to provide FPS style mouse input for a web app. Cross-browser solutions required a Java-applet or additional plugin to "capture" your mouse input. Hardly ideal solutions. A new W3C draft proposal, the Pointer Lock API [1], hopes to standardise this issue.

 The Pointer Lock API is for mouse input what what input.focus() is for keyboard input... It "Locks" your mouse pointer in place, limiting pointer movement to an area, ensuring the pointer input stays relevant and doesn't go off the edge into another window. Mouse movement values (not just co-ords, but the mouse deltas also) will be included in the mousemove event. This combined with hiding the cursor is what is required to code FPS style input (amongst many input schemes) for your app.

Since this feature is ripe for abuse, the specification demands that the user is first asked if they want to lock their mouse. The lock can be released by pressing the "Esc" key. The "Esc" key event would have to be promoted to a top-level browser event whose default action cannot be prevented.

The discussion about abuse is moot I feel. The HTML JavaScript "window" object allows you to resize and re-position a browser window arbitrarily. So whatever abuse a mouse lock feature would enable has already been enabled by the window API - remember "Rick Rolling"? (a video played a particularly annoying Rick Astley hit and any attempt to close it was prevented by the script simply moving the browser window away from your franticly flailing mouse pointer). The fact is sites that chose to exploit that feature in an abusive manner only got visited at most once. It might be good for a gag, but you can only fool them once. Also, the Pointer Lock API at least has the "Esc" hatch, making it safer than the existing window API anyway. And since the pointer can't go outside the locked area means the script can't go clicking on other windows.

Have a  look at the html5Rocks article for a more technical overview [2]

Links:
[1] http://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html
[2] http://updates.html5rocks.com/2012/02/Pointer-Lock-API-Brings-FPS-Games-to-the-Browser