This extension finds out information about domain names including the name servers associated with the domain, the domain Administrative and registrar, Billing and Technical contacts with email and postal addresses.
After clicking on Whois-Lookup, it will show the result in popup window without opening new tab. You can search for Whois by entering the domain name.

This extension is also available for Google Chrome browser at below link:
https://chrome.google.com/webstore/detail/miaeabadkjiniibecbdcmopdaecfmabd

This extension is also available for Opera browser at below link:
https://addons.opera.com/en/addons/extensions/details/whois-lookup/1.0.0/