If Hardware Acceleration is not supported by PureBrowser,
it should be disclosed to future purchasers before they buy.
Because this means you can’t watch a video and search the web at the same time,
like most people do, without experiencing sluggishness.
Everything freezes for seconds when you accidentally start a 2nd video.
This happens a lot while queuing up the next video in a new tab,
In Purebrowser, about:config, enable layers.acceleration.force-enabled
and it still requires 100% cpu to watch youtube videos.
Hardware Video Acceleration is still touch and go on Linux in general (especially on ARM). Things have gotten a lot better with dedicated video applications but browsers are a whole 'nother ball of wax. Neither Firefox nor Chromium support it in Linux. The latter even has a special build in some distros to enable it. Check out this entry in the Arch Wiki about Application Support.
To help with this issue, Mladen wrote this PureOS Wiki entry to allow web videos to be opened in GNOME MPV from PureBrowser. its a lot less resource intensive doing so through MPV than a browser, even at 720p+.
The sluggishness I was experiencing was caused by infowars.com.
If you leave that site open in a browser tab, it turns your computer into
a content distribution node. My machine had sent 3GB of network data.
As soon as I closed that tab, the network traffic stopped and CPU lowered
40%!
I tend to have 30 tabs open at a time so it took me a while to find out who was causing the issue. I stay the hell away from infowars now.
Not a solution for everybody, but the main reason why I use Brave on my Librem 13: HOWTO: Brave browser installation (see post #12 for current instructions)