I'm going to guess that you're using the 64bit image? If so, this is unfortunately a bug in the Firefox ESR package for arm64. The upstream Debian bug is https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=906570 - A possible workaround is to use Chromium, though you will need to make a couple modifications to the launcher as Chromium doesn't like being run as root, or you will need to launch it from the command line to pass the arguments.

Also, can you please give the output of "apt policy firefox-esr" so I can see which version of firefox-esr you're running?

Is this still an issue for you? The latest firefox-esr packages are working here on both arm and arm64.

Due to the age of the OS (Kali Moto [v1], Kali Safi [v2], Kali Rolling <= 2019.2), these legacy versions are no longer supported.
We will be closing this ticket due to inactivity.

Please could you see if you are able to replicate this issue with the latest version of Kali Linux - https://www.kali.org/downloads/?

If you are still facing the same problem, feel free to re-open the ticket. If you choose to do this, could you provide more information to the issue you are facing, and also give information about your setup?
For more information, please read: https://kali.training/topic/filing-a-good-bug-report/