The browser in raspbrain is so much faster and won’t lag while playing YouTube.
I have found lagging while watching YouTube in Firefox.
Audio and video won’t synchronise.
Any solution?
Thanks.
The distro is raspbian, not raspbrian. I’ve also had the same problem. You could try Chrome, as it can handle flash with ease. 
Hope this worked!
Dont you mean Chromium? Or is there a version of Chrome for ARM and Mate now? I had just looked for this myself.
Yes. I meant Chromium. Sorry.
But i read that people having problem with chromium.
Oh! So that’s why there are lots of topics about Chronium 
Try installing the Midori browser, i’ve had very good luck with it.
To install Midori type the below command in a terminal window:
sudo apt-get install midori
or you can install Epiphany which is what rasbrain uses
sudo apt-get install epiphany-browser
Midori and Epiphany are very similiar
I didn’t like that Midori didn’t have the menu bar enabled by default, its easy to re-enable it though.