Hi shorty123
If you’re planning on installing software – at present moment or in the future – you should use the distribution package manager. Since Whonix is based on Debian you should the official Debian package manager called) APT
When you went to the Mozilla site you saw this mentioned which was referring to the above.
Use your system’s software package manager and ensure that PulseAudio is correctly installed.
Unfortunately its not always that easy. To get audio working in Whonix 13 you may have to do some troubleshooting. That’s why awokd mentioned you may want to try Whonix 14 (audio should work). However its important to add that Whonix 14 is still in testing. There a a few issues that need to be ironed out but they are not security related.
https://forums.whonix.org/t/whonix-14-release-blockers-status-of-whonix-14-development/5111