WHOIS Lookup di Kemal Goksu

WHOIS Lookup is a lightweight Firefox extension that shows registration details for the domain in the active tab. It queries the registry's RDAP endpoint when available and falls back to a classic WHOIS web service.

WHOIS Lookup add-on detects the domain in the active tab, shows the registrar, creation/update/expiration dates, nameservers, and domain status. Caches lookups locally for one hour. Indicates when a domain may be available, opens one of 10 configurable popular registrars for a final availability check.

Lets you clear cached lookup data from the settings view.
Does not cache lookup results from private browsing windows.