Known issue: Filter memoization will, sometimes, kill Safari-based browsers for as-yet-unknown reasons - it appears to cause the the getImageData() invocation on line 595 in mixin/entity.js to go from taking a a handful of milliseconds to over 5 seconds, but only after an element's memoizeFilterOutput flag has been set to true.
For now, if Scrawl-canvas detects that the user is viewing the canvas in a Safari-based browser, it will ignore requests to memoize filters. Use cache output functionality instead to improve render speeds.
Touch test: not required