Searching Google for "download firefox" gives me an ad for mozilla-firefox.godownload.net at the top of the results.
That page says:
"This site distributes software [...] via GoDownload Manager which [...] will make recommendations for commercial offers that you might be interested in. The additional software may include toolbars, browser add-ons and other types of software applications."
Basically, they're squatting searches for free software like Firefox, and they bundle their downloader tool which tries to convince you to install other stuff.