The same happened to me, though I think his point would have made more strongly if he had acknowledged at any point that he was running a beta version. So normal people still have some time (6 weeks or so?) before this is an issue for them.
It will be an issue nevertheless, though.
Anybody still wondering why users are scared to upgrade stuff?
Isn't this cat-and-mouse issue between extension vetting and new Firefox versions always present when running Firefox beta? I assumed it was one of the tradeoffs, i.e., parts may be broken...?
No. This is a new feature that disables all unsigned extensions. It will be in the next version of the normal Firefox. The setting to allow unsigned extensions will be removed in the version after that (or so I've read).
Chrome has done something similar for a few years now, but (unlike Firefox) Chrome allows white-listing extensions via Group Policy.