These similar testcases involving stroke methods cause Firefox to hang till the user will be forced to restart the process. Peers like Google Chrome seem to reject or ignore those large values. // exhausts CPU o0 = document.createElement('canvas').getContext('2d') o0.mozDash = [1,0,1,1,1] o0.strokeRect(0, 0, 0, 8589934591) // allocates all available memory o0 = document.createElement('canvas').getContext('2d') o0.mozDash = [0,1,0,0,1,0,0,1,0,0] o0.rect(0, 0, 0, 67108865) o0.isPointInStroke(0, 0) // exhausts CPU o0 = document.createElement('canvas').getContext('2d') o0.bezierCurveTo(9.335285731017646e+306, 0, 0, 0, 0, 0) o0.stroke() Tested with https://hg.mozilla.org/integration/mozilla-inbound/rev/f7496fddb076 and Firefox 22