What would removing Firefox accomplish? Why would students not just download one of the bazillion Chrome VPN addons? Or regular VPNs that they can just turn on and off? How is _removing Firefox_ a solution?
What these schools need is to set up sensible group policies. Managing BYOD on a school with kids (as opposed to grown-up people whose jobs are on the line) is simply impossible.
I think the poster was talking about two separate schools. One which doesn't allow BYOD and tackled the problem by removing Firefox, and a second where the poster works at which does allow BYOD and therefore removing Firefox is not an option.
What these schools need is to set up sensible group policies. Managing BYOD on a school with kids (as opposed to grown-up people whose jobs are on the line) is simply impossible.