For those of you who aren't meganerds, here are a few links to help you understand what we're talking about. :-)
Flash, the technology used to display the Tree Mode, is a proprietary browser plug-in that has a long history of poor performance on some platforms (Mobile devices, OS X, and Linux).
HTML5 (and the related technologies) are industry standards that are built right into your web browser.
When the HTML5 technologies are properly implemented, they provide faster and more reliable results with lower overhead.