YouTube is blaming that Firefox delay people been talking about on adblockers. - eviltoast
YouTube blames ad blockers for slow load times, and it has nothing to do with your browser
www.androidauthority.com
YouTube has clarified in a statement that users who use ad blockers will have a suboptimal experience regardless of their browser.

This delay isn’t exclusive to Firefox, it’s in any browser where a user has enabled adblockers including in Chrome. Disable the adblocker and this delay magically go away. This was done on purpose.