For my money, they oughta make Canvas click-to-play as well, since the rendering speed in Firefox is unbelievably slow and the javascript behind it is so frequently written to hog up 100% of the CPU it's hard to even know what you're looking at if you accidentally stumble across an HTML5 page in Firefox, before your system grinds to a complete halt. It's funny how people blame Flash for slow websites when what they should really blame is bad coding practice, which can just as easily show up in JS (and does). To take it further, it's pretty rare for Flash code to bootstrap a huge set of libraries to do some petty effect - and if it does, the plugin doesn't freeze the browser preload while waiting on them. Whereas a 150k JS file that includes jquery and a bunch of other junk which probably isn't necessary (but makes coding some effect that much easier for bad programmers) can bring a website to its knees before the first line of text is delivered in the browser.

Again, don't blame the tools; blame the tools who use them.