<html> <body> Firefox: <a href="javascript:noCrash()">no crash</a> | <a href="javascript:crash()">crash</a><br/> <canvas id="foo" width="200" height="200"> </canvas> <script> function d(lineWidth){ var c = document.getElementById("foo").getContext("2d") c.clearRect(0,0,200,200) c.lineWidth = lineWidth c.beginPath() c.arc(100,100,80, Math.PI, 2*Math.PI, 1) c.stroke() c.beginPath() c.arc(50,50, 20, 0, 2*Math.PI, 1) c.stroke() c.beginPath() c.arc(150,50, 20, 0, 2*Math.PI, 1) c.stroke() } function noCrash() { d(Math.random()*20+5) } function crash() { d( '_' ) } crash(); </script> </body> </html>