I abandoned pure standards-respecting HTML5/canvas while working on a similar tool (for pixel art, not general drawing), for reasons which will readily become a

I abandoned pure standards-respecting HTML5/canvas while working on a similar tool (for pixel art, not general drawing), for reasons which will readily become apparent when you try to save a file... then load one. Flash is still quite useful because desktoppy apps have legitimate needs which are thwarted by the browser's rather uptight security model, but are mostly satisfiable with Flash's controlled way of enabling them.