

There isn’t a browser suitable to replace Firefox in the official Debian apt repos.
However, as far as I can tell, Mozilla’s recent Terms of Use apply only to the Firefox builds downloaded from Mozilla, not to the built-from-source versions that you get from the Debian archive using apt.
You can use the Debian build under the terms of the Mozilla Public License. Read /usr/share/doc/firefox-esr/copyright for details.
Sony used to make compact variants of their flagship Xperia phones. Good specs. Good battery life. Good camera. Good display. Good sound. Good reception. Headphone jack. SD card slot. Unlockable bootloader, so they could be de-googled.
Sadly, the “compact” models grew slightly larger with each model year, and even a not-so-compact one hasn’t been released in a while.