Firefox fingerprinting protection breaks mouse event handling

[eternal-sorrow]

I noticed some years ago that some html5 games do not work correctly in my browser. The problem is always the same - a click at any point in the canvas always registers as a click at one specific element on the screen. I couldn't pinpoint the issue correctly so I didn't know where to ask help for this, so I just shrugged back then, started Chrome and the game worked as expected in it. Recently I decided to investigate and after a debug session I found that the game in question uses CreateJS and soon I found the culprit:

EaselJS/src/easeljs/display/DisplayObject.js

Line 1326 in c716bf0

var hit = ctx.getImageData(0, 0, 1, 1).data[3] > 1;

CreateJS uses getImageData canvas method to detect a hit on an element. With fingerprinting protection enabled this method returns random noise on Firefox. So CreateJS always detects a hit on the first displayed object, no matter where the click actually happened.