Floorp. It's open source fork of Firefox made by mostly Japanese developers. It's noticably faster, privacy focused than the original and have more customisation options.
2.5. Floorp is not completely open-source same. Floorp's a part of codes are protected by copyright law and is not licensed under an open-source license. You may not use part of Floorp's code in your own projects without permission from the Licensor.
2.6. If MPL2.0 or any other open-source license notation is present in the file, the file is available as open source.
It seems like their modifications and the resulting application are proprietary.
The MPL is an open-source license designed to protect its own code. If you modify MPL code, you need to publish those modifications under the MPL. That's the focus of the license. There's no "viral" requirement to affect the licensing provisions of the rest of your code.
That looks too good to be true, do you use it? I've been not as happy with Firefox lately. They keep a record of all my bookmark history and update so often it makes your head spin. I couldn't tell if the updates are because they're doing something or it's so popular that they need to do that for security.
Not happy with Firefox ? For a more privacy friendly Firefox fork check LibreWolf : https://librewolf.net You don't have to remove Firefox, you can run both at the same time.