I uninstalled Flash a couple of months ago, and only rely on HTML5, which plays by default. I use this in Firefox all the time. However, I still prefer ClickToFlash in Safari because it is so easy to right click directly on the "video screen" and select "Download Video," if I want to download one. I don't download very often, but it's a really nice feature to have with a single right click and left click when needed. In ClickToFlash, it is also somewhat easier to change video sizes (240p, 360p, 720p, etc.) in the upper-left corner of the "video screen." Uninstalling Flash also disables all (or some?) Flash-based advertisements. Finally, ClickToFlash is the only way my ancient Snow Leopard version of Safari can play YouTube videos anymore. 🙂 That being said, I will continue to use ClickToFlash even in the newest versions of OS X.