Cert check doesn't need to connect to any url to fail. It's just the cert's only expired 20 hours ago, so this issue is currently only affecting approximately 83% of users who happen to be checking at a time of day that has already passed, over the next 4 hours that will go up to 100% (ignoring users who receive a fix before it breaks).
i passed my `app.update.lastUpdateTime.xpi-signature-verification` time and still had no issues with addons failing, so i dug into it a bit.
turns out i had `xpinstall.signatures.required` set to `false`, which i'd done to get an older extension working in the past (and subsequently forgot to set it back to `true` later). so i don't think my install of firefox has been checking addon signatures for a while now, which is why my addons remained functional (with other security implications of course).
i didn't immediately find where the cert was stored (to check it's expiration date) however.
