Mozilla is currently developing an open standards-based Flash renderer called Shumway. https://developer.mozilla.org/en-US/docs/Mozilla/Projects/Shumway Available as an extension [http://mozilla.github.io/shumway/extension/firefox/shumway.xpi here]. ''< click to launch the add-on installer.'' ''It seems to work fine on YouTube videos in the Firefox 31 release version, although it is somewhat CPU intensive.'' And also available in the Nightly development versions. http://nightly.mozilla.org/ Feel free to try it out, but make sure you install it into its' own Program Files folderset and make sure you create a unique Profile for use only with Nightly. If the same Profile is used with both Release and pre-release versions problems sometimes arise after switching back and forth between different versions of Firefox. Basically, Nightly is like 18 weeks ''(at a minimum)'' removed from becoming a release version, but some projects stay on Nightly for a longer time as they are being developed. That happens to provide as many user / testers as possible, by not resorting to a separate development trunk version.