When I've seen this effect in Mavericks 10.9.4, it's almost always been while watching online videos in multiple tabs on Firefox.....and the cursor appears to disappear BEHIND the active window in the browser....I recover to have the cursor appear on top of the active window again by moving the cursor (in the blind) over to the far right of my screen where the dock hides. Once the dock pops up, the cursor is back where it's s'posed to be again -- until the next event.
Perhaps it's related to the browser? or to the video player? or........?
