I was referring to the machines they were preventing the installation of Firefox on.
For BYOD, I don't know what you're gonna do. Many students have smartphones too (some with tethering), and you can't control what they look at on those either. Plus, even if the school could somehow magically lock everything down 100% within the confines of the school building, the students can still get access to whatever at home, or using coffeeshop WiFi, or whatever.