Almost all previous web panorama viewers have been plug-in based, be it Java, Flash, QuickTime, et cetera. With growing browser support for WebGL, this is no longer necessary. As of writing, approximately half of the browsers currently in use support WebGL. With proper graphics drivers, recent versions of Firefox and Chrome support WebGL by default. In addition, recent versions of Safari and preview versions of Opera have WebGL support, although it is turned off by default. The notable exception to WebGL support is Internet Explorer, with no versions, including the preview release of IE 10, having support. Although large swaths of Internet users run browsers that do not support WebGL, support is steadily growing. Plug-in based solutions may have better support today, but WebGL and standards based development is the future.
One last feature that gave Flash an advantage over HTML5, was full screen support, but in the past few months this has changed. While still an early draft, the Full Screen API allows for web applications to programmatically enter full screen much in the way Flash does, allowing for a more immersive experience. When development on Pannellum started, this was not the case, and I originally implemented more limited full window support by opening a larger popup window. This original method is still supported for older browsers that support WebGL but do not support the Full Screen API.