Answer:
Google Analytics.
Step-by-step explanation:
Google Analytics is a tool from Google that records all kinds of information about the visitors to your Web site when it's configured.
It will show you where they are from, when they visited your Web site, how many times they visited it, how many pages they visited and so on.
StumbleUpon has nothing to do with that, it's like a recommendation tool (Hey!, I found this, check it out).
Yahoo! is a search engine (that started way before Google)
Mozilla is the maker of a Web browser (like Google's Chrome) called Firefox.