Notably, the same results are available merely by going to http://www.tcpiputils.com/ and typing in the URL you're curious about, although that would take a moment longer.
The Add-on technically does work, but the information displayed is translucent to such a great degree that the underlying web page "bleeds" into the "IP Address and Domain Information" window. In short, it's really, really distracting -- and difficult, at least for me -- to look at the readouts. I can't imagine why the developer would choose this on purpose, and I don't think it's a bug, but intentionally programmed.
By the way, a due diligence check of the support site link shows that it links to their site, but there is no support section on that page, nor on that site, that I was able to find.
The Add-on will embed graphic PPC/CPM advertisements within the results it shows you. I wasn't able to find any warning, setting, or explanation anywhere in the product that offered an explanation as to how the ads do or don't effect me as a user. They simply appear. That seems like a privacy issue that should be addressed.
Based on the visual design issue above and my inability to understand how my browsing privacy might be effected, I chose to uninstall the Add-on.