I did nothing to “tweak” Firefox. I did use their binary installer for Linux because I wanted the latest updates and Slackware is a bit conservative with its packages.

My Linux box at work is an HP laptop from several years ago with a pretty basic business class AMD graphics card in it, I did have to install AMD’s binary drivers on this machine.

And, using Slackware, it’s X. Not sure if Wayland is easily installable or not on Slack but it’s certainly not part of the base install or supported by Patrick.

Firefox is the only piece of my install that isn’t part of official Slackware-CURRENT.

Other than running it in Windows all of my other computers that use Firefox are running stock, no fancy desktop versions of Slack or OpenBSD. I use calm window manager on both. (Sorry, this contradicts an earlier statement, I also had to compile and install Calm on Slackware from source, everything else is just part of the supported packages for CURRENT)

Maybe my low resource OS’s help?

Thank you for the great info! I bet it's the AMD graphics card helping. I know Nvidia is a mess (and requires the aforementioned tweaking). I'm glad it's working well for you and I'd love to test a setup like this as I really want off Chromium but haven't had an equal experience with Firefox (on OS X and Linux with Nvidia cards).

In my Linux and Freebsd boxes I have to install the proprietary driver for Nvidia cards to have full hardware acceleration.

You think Firefox having shitty video rendering performance is somehow because Google tweaked YouTube not to work? Are you kidding?

You don’t think Google could make YouTube work better on Firefox? Of course they could.