Hi all.
I've discovered Vivaldi Browser for arm. A fork of Chromium.
There is a armhf version and a arm64 version.
Youtube playback with this is a lot better. I've tested it on the NanoPi M4.
The same video in Chromium had 2/3 dropped frames. (10 frames/s) 1080p video
With Vivaldi browser you get 1/3 dropped frames. (20 frames/s)
A lot better experience.

Here you can download it.
https://vivaldi.com/nl/blog/snapshots/vivaldi-1-15-rc-2/
 

Here the source where I found it. From Meveric @ Odroid. Also explanation of how to install. No wget, and change filename to the file you've downloaded for gdebi. Or use gdebi package installer.(not tested)
https://forum.odroid.com/viewtopic.php?t=29229

I tried in armhf on the M4 in armhf Lubuntu, worked great. Also tried the arm64 in Armbian Stretch. Also great.
I didn't find any posts about Vivaldi in the Armbian forum. I thought it could be helpful.
Cheers

Thanks NicoD I'm trying it out, I like Brave Browser but can't find it for Arm and so far Vilvaldi seems to be good! I do prefer Firefox but it does not work well on this Debian Buster! I must move back to Ubuntu!