Have you thought about posting on the PaleMoon forum? You'll need to create an account and think of a user name, but that's pretty much standard. I've had a quick look on your behalf, and this thread may be of some interest:
Code:
http://forum.palemoon.org/viewtopic.php?f=15&t=8969&p=59792&hilit=flash+pluginslow#p59792
The mention of Flash "ESR" lead me here (2/3rds of the way down):
Code:
https://www.adobe.com/products/flashplayer/distribution3.html
I have also experimented with the Flash Plugin disabled (selected from "Tools > Add-ons") - The BBC news site won't play any clips without it, but many "tube" sites now offer HTML5, and work fine. Usually if there is a problem with Flash it comes up with an error message, rather than just doing nothing.
But further to my first reply, I find that the "loading circle" delay doesn't always occur - there seems to be no rhyme or reason to it - sometimes YT clips will play straight away, other times I either have to wait for 10-20 seconds or hit "Refresh".
Dunno if any of this helps?
TFP