The proposed solution to Firefox's certificate expiration issue won't work on Debian because data reporting is disabled for Debian builds of Firefox. A workaround mentioned in passing here appears to have worked for me.
The workaround consists of visiting https://storage.googleapis.com/moz-fx-normandy-prod-addons/extensions/hotfix-update-xpi-intermediate%40mozilla.com-1.0.2-signed.xpi directly and allowing Firefox to install the xpi file.
Drive carefully. Your mileage may vary
