Since I have switched over to firefox, I miss my browser extensions package that i developed for Sleuth.
Firefox developer tools have similar features now for some things, but I always missed my right click whois tool where I could highlight an ip in the page and have it give me the info on it. A quick search of the net today turned up a nice pre-made whois firefox extension written by FirefoxWiz that does just this.
Note that this tool was released in 2008. In order to get it to work with current versions of firefox:
rename .xpi to .zip and extract to a local folder
open install.rdf in notepad and edit the em:maxVersion (i set mine to "22.0.0.*")
re-zip the files making sure that the install.rdf and files remain in the top root of the archive.