Firefox may be incompatible with DFSG and probably other similar principles and TOS.

From the bug report:

The new Terms of Use, from what I can see, are in violation of the DFSG points 5 and 6:

5. No discrimination against persons or groups

Rationale:

The terms of use grant Mozilla the right to terminate anyone's access:

        Mozilla can suspend or end anyone’s access to Firefox at any
    time for any reason


  

https://www.mozilla.org/en-US/about/legal/terms/firefox/#mozilla-can-update-or-terminate-this-agreement

6. No discrimination against fields of endeavor

Rationale:

The terms of use don't allow you to use Firefox to break the law. While this seems a reasonable term, it wouldn't be so reasonable for a disident in an oppressive country.

        you agree that you will not use Firefox to [...] violate any
    applicable laws or regulations.

  

...

Apart from these violations of the DFSG, Firefox has now permission to leak user data to Mozilla, and who knows who else they decide to sell it later. This is a security bug.

        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 [...]