What do you see here? see screenshot

Mine looks like that. I get about 30 sec of audio then nothing.

and only for sling tv. Youtube works fine

Yeah, this issue is coming up far too often in the forum for me.  ;-))

How about posting a screenshot from device manager showing you audio device and driver version?

Does it still happen in Troubleshoot Mode?

Yes it does it in troubleshoot mode as well.

Anything media related in the Web Console ?

• https://firefox-source-docs.mozilla.org/devtools-user/web_console/