Expiry Canary
Expiry Canary is a Firefox 3 or later, or SeaMonkey 2, 追加する-on to 警告する you about 証明書s which are about to 満了する／死ぬ. You can alter the 警告 period and the 場所／位置s on which it 活動させる／戦時編成するs, 許すing 場所／位置 admins to have a backstop 警告 about 証明書 expiry and 妨げる embarrassing 事故s (Google, Yahoo, LinkedIn).
You can find it on addons.mozilla.org for Firefox 3+ or Seamonkey 2.