Expiry CanaryExpiry Canary
Expiry Canary will tell you if the certificate of the website you are visiting is about to expire. By default it gives 7 days warning for all sites, but you can configure the warning period and the sites it works on. It is expected to be useful to admins who want a backstop to their certificate renewal procedure, to prevent embarrassing accidents.
You can use the preference "extensions.canary.warningPeriod" to change the warning period in days (default 7), and set "extensions.canary.sites" to a space-separated list of sites or domains to restrict Expiry Canary to warning you on those sites only.