I use it and contributed the suggested $5.00. It is a great add-on for Firefox and does a pretty decent job. Could not even give you an idea of how many people use it, but do know it is talked about around here frequently.
I think it's against the forum rules to talk about it, so I get this thread will see a swift exit before long. Either way I wouldn't disable it even if doing so helped save starving Africans.