HTML5 shadowblur Significantly Slowing Down Framerates...

Good News! Bionic Battle Browser Bots is a featured game once again on Google's Chrome Webstore. Along with more players comes more feedback and large numbers of users are reporting that the game can drop to unplayable framerates of 2 fps or so and the background tiles appear with blurred borders. I have traced this to the HTML5 shadowblur properties of the shadow API. This cool feature helps different html5 elements in the game look nicer with blurred shadows and not much extra graphic or coding work, BUT.... The game seems to be taking a big performance hit from using it. So for now, shadowblur is off and framerates are back up to a consistent 60 fps. Maybe in the future when browsers can handle this html5 feature better, I will turn it back on. Also note that Chrome and Safari seem to be the ones with performance issues. IE and Firefox seem to handle it fine. For your reference, here is the chunk of code:

context.shadowBlur = 4;
context.shadowColor = 'rgba(255, 0, 0, 0.5)';