The RESET error indicates that Firefox was instructed to stop trying to connect to the site (RST response). This could come from the site itself, or from an intermediate router, or from a filter/proxy or from security/parental control software. Unfortunately, this can be difficult to track down.

Can Firefox connect to other Google sites, the problem is only with YouTube?

Can the Microsoft Edge browser connect to YouTube normally?

Microsoft Edge won't connect either. I have Norton firewall and virus protection. Trying to see if that is the cause. I turned it off completely and nothing changed. Maybe my ISP. Still looking.

Turned on Mozilla VPN and now I have access to youtube. A different IP address solved the problem apparently.