It’s quite a bit more then that actually… https://www.mozilla.org/en-US/about/legal/terms/firefox/ states

You give Mozilla all rights necessary to operate Firefox, including processing data as we describe in the Firefox Privacy Notice, as well as acting on your behalf to help you navigate the internet. When you upload or input information through Firefox, you hereby grant us a nonexclusive, royalty-free, worldwide license to use that information to help you navigate, experience, and interact with online content as you indicate with your use of Firefox.

A very broad, basically unrestricted license to any and all input you make (mouse clicks, keystrokes, file uploads, …) for a very vague purpose.

Additionally, it says you ought to follow the Mozilla Acceptable Use Policy which includes not at all problematic things like

• no illegal stuff. Illegal where? We don’t know! (Do anything illegal or otherwise violate applicable law)
• sending a message to someone without asking first. How? We don’t know! (… send unsolicited communications …)
• no troll account, no parody accounts (Deceive, mislead, defraud, phish, or commit or attempt to commit identity theft)
• no illegal gambling. Again, illegal where? Who knows! (Engage in or promote illegal gambling)
• don’t buy controlled drugs, even if a doctor prescribed them (Sell, purchase, or advertise illegal or controlled products or services)
• no porn, no LGBT memes (Upload, download, transmit, display, or grant access to content that includes graphic depictions of sexuality or violence)
• no torrents, no youtube downloads (Violate the copyright, trademark, patent, or other intellectual property rights of others)

What a fun and totally sensible list of restrictions for a “free” web browser to have.