Once we find a good way to detect versions of websense, we'll want to message users who have incompat. version letting them know they should upgrade or uninstall the old websense version.

Hey felipe, is this something we could do through the system addon?

Yeah it's doable, but it will involve a special process for localization.. And system add-ons currently hit only 55% of users, so a dot release might be better.. It will depend on the timing and the number of remaining people stuck with websense. We'll know better about this with the release of 47.0.2 now. My suggestion is to write it a system add-on, and then we can decide about shipping it over-the-air with GoFaster, or built-in with a dot release.

I believe what was being referred to in the mail list is... "We've had the ability in product to inform the user that their platform is no longer supported along with a link for more information for a while now and this is what is being referred to."

Too late for firefox 52, mass-wontfix.