Cool! I wrote a similar extension for Chrome that simply enforces a user-adjustable maximum cookie lifetime (e.g. 21 days instead of 10+ years...). This seems to provide a good balance for login cookies that you don't necessarily want removed every session.

https://github.com/semenko/chrome-limit-cookie-lifetime

https://chrome.google.com/webstore/detail/limit-cookie-lifet...

(And the same for Chrome's ever-present history:

https://github.com/semenko/chrome-limit-history-lifetime

https://chrome.google.com/webstore/detail/limit-history-life... )