this does not show the current IP address but makes a nslookup for the domain name. the dnslytics information is interesting, but to me the name and description is wrong/misleading

Correct extension for Firefox 57+, but not as good as Flagfox

Although this IP finder works, it opens a new tab, showing, essentially, the same information that the icon's pop-up does. In other words, not only is it redundant, it takes up additonal resources, unnecessarily. Since the tab "feature" can't be turned-off, this is no better (and, arguably, worse) than accessing an IP finder on the web. I removed it from my add-ons.