See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

thank you for the quick reply

Drivers are up-to-date.

Turned off the accelerator and the webGL to true; still getting that distorted audio issue.

A post was flagged as Solved Problem. Please remove that flag. If you don’t, others that can help may not read this post.

Go to that message, and use the Undo link to its right.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

Booted up in Safe Mode. Audio distortion is still present. And it's just with Facebook post video.

I do not have Facebook. Have you checked their support?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia