Saving web worker'd gif via PhantomJS.
Slight modification to the original page converts the gif result to a base64 global for PhantomJS (example).
PhantomJS grabs that and sends to stdout. Decode that and then have a gif party.
$ phantomjs capture.js | base64 --decode > what-a-cool.gif
Probably requires a >2.0 version of PhantomJS.