This is highly ungood, of course. The failure to notice an upcoming expiration is terrible in itself, but I suppose we can sort of almost empathize with how such shit may happen. The failure mode is inexcusable. Someone somewhere sometime must once have made a decision, "this will be the right way to fail", or - worse - developed the addon certification system and deciding it didn't need no stinkin' graceful degradation route in case of disaster.
Still, it's no worse a calamity than most everyone else presents to the world from time to time. I shall stick to my Firefox, partly influenced by the complete absense of any viable alternative out there.
By the way: Writing this a few hours after midnight, May the fourth, local time. Every single one of my 33 Firefox addons is active and working just fine. Wating to see. Breaking out my Waterfox, just in case.
[Edit: May fifth -> fourth]