Prompt before allowing Canvas isPointIn*() calls
There were some changes to the HTML5 canvas object. I think toBlob() was added, and possibly other extractors as well: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D
There is now also a hint that JS wants to read the canvas. Probably irrelevant to us, but worth looking at in more detail: https://bugzilla.mozilla.org/show_bug.cgi?id=884226
There's also something called HitRegions. I'm not sure what these are at all: https://bugzilla.mozilla.org/show_bug.cgi?id=966591