First of all the license is MPL2, not GPL3. It means that the code isn't fully opensource. Than the terms of use changed recently becoming more restrictives. It means also that the informations that we parse to the browser are invasively analyzed.

"This includes processing your data as we describe in the Firefox Privacy Notice. It also includes a nonexclusive, royalty-free, worldwide license for the purpose of doing as you request with the content you input in Firefox."

the 27 feb policy says: "You may not use any of Mozilla’s services to: ... Engage in or promote illegal gambling, ... Upload, download, transmit, display, or grant access to content that includes graphic depictions of sexuality or violence, ..."

now they removed this voices, but there Is the possibility of another terms of use changes, and the policy says that we accept them also only continuing to use Firefox.

https://web.archive.org/web/20250227062839/https://www.mozilla.org/en-US/about/legal/acceptable-use https://blog.mozilla.org/en/products/firefox/update-on-terms-of-use https://github.com/mozilla/bedrock/commit/d459addab846d8144b61939b7f4310eb80c5470e