The pointer lock's specification of MouseEvent.movement{X,Y} [ http://www.w3.org/TR/pointerlock/#attributes-1 ] says: "When unlocked, the system cursor can exit and re-enter the user agent window. If it does so and the user agent was not the target of operating system mouse move events then the most recent pointer position will be unknown to the user agent and movementX/Y can not be computed and must be set to zero." We don't do this. We should do this. Steps to reproduce: 1. Go to http://people.mozilla.org/~eakhgari/pointerlock.html 2. Open the web console (CTRL + SHIFT + K) 3. Move the mouse outside of the browser window. 4. Move the mouse back inside the browser window at a different place than where it moved out of the browser window. Note the large movement reported in the web console log. Expected result: No large movement, we should report (0,0) movement for the move that enters the browser window.

Invalidate nsEventStateManager::sLastRefPoint when the pointer leaves the window, detect that, and cause mouse movement to be 0 upon the next movement.