I've had Ghostery installed on Firefox for years now and it's served me well, but I just removed it & won't be back—Ghostery has become increasingly commercialized and with its latest update is repeatedly intruding with pop-up ads of its own trying to hock its monthly paid "premium" service. Ghostery's become an ad-blocker that—bewilderingly—shows you ads; moreover, there's no functionality it provides that other privacy add-ons don't/can't.

Do yourself a favor and skip clicking the install button & just close the tab.