No, the culprit you are losing add-ons isn't your computer, or maybe your old FF, or dropping of Webextensions API. Twitter, Reddit, everyone is wondering what is going on. This Armagadd-on 2.0 has a simple explanation: Mozilla forgot to renew certificates, and so add-ons are failing like if they were not properly signed, because technically they are not. Even signing of new add-ons is down (see comment 9). Great weekend at Mozilla HQ!
Some workarounds, until they clean up the mess, include playing with the computer clock (NTP? forget it) or disabling signature checks (not possible in default releases).
User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0
Steps to reproduce:
Wait until it's past midnight on 2019-05-04 UTC.
Actual results:
All addons got disabled due not having valid signature.
Expected results:
If the signature was due to expire, it should have been renewed weeks ago. Not all extensions were disabled. Fakespot and Google Scholar Button were left in their disabled state.
Some reports on reddit says that they had their clocks a day forward, but they may be just early canaries for the actual widespread issue.
Going backwards in time allows installation from AMO (Mozilla Add-ons) but do not remove the unsupported mark from the add-ons already installed.
https://bugzilla.mozilla.org/show_bug.cgi?id=1548973
Workaround: Go to about:config and set xpinstall.signatures.required to false
(Score: 1, Informative) by Anonymous Coward on Sunday May 05 2019, @12:14AM
That won't do you any good. My Firefox has been running for a few weeks and just got hit by this drive-by extension-disabling. Bastards.