There still is a Flash fallback for ancient browsers that do not support the "video" tag. Some older browsers (such as Firefox 3) that support the video-tag but do not support either the MP4 or the WebM video codec may show an error. In that case, please go to our youtube channel to watch the screen casts.
--- Update 2013-07-24
Since Firefox 21, MP4 is supported on Firefox if you're on Windows 7 or higher. There may be problems with colors that are resolved if you go to about:config and set