Flash is a Firefox plugin made by Adobe, not Mozilla. It's not installed by default, it's added when you install Flash on your computer. If you want it off, just uninstall Flash from your computer or type "about:addons" into your address bar and disable the Flash plugin yourself.
Actually the article is about add-ons, which according to FF terminology include extensions, themes, and plugins.
Of course there's not a chance that Mozilla will stop supporting Flash in its browsers, but I thought it was a funny comment on the performance of HTML5 video/interactive content vs Flash.