The need for killswitch I think is self-inflicted.

* Mozilla has a track record of forcing unwanted changes on its users. What with Pocket, data collection and telemetry defaults, sponsored links throughout the UI, all the good stuff.

* The enduring users are more likely to want to revert any Mozilla default the moment it's introduced. (This is why Firefox has disproportionately many projects to un-Mozilla the thing: Arkenfox, BetterFox, LibreWolf, Waterfox...)

This is from the annoying (sure hope so!) sporadic Firefox user who was actually pleased by the news. Honestly, I saw it and though: wow, Mozilla giving the tiniest part of control back to the user, that's actually good! Short-lived as the excitement was, in these fading moments of Firefox I'd like to see more of this and less of the user-hostile thing please.