So I'm no expert but I believe there are actually two different notions of hardware acceleration at play here:
1) HW accelerated rendering in Firefox, which despite being unfortunately disabled by default on linux can in my experience be enabled (on about:config) without issues. This makes the experience of scrolling much smoother, so I usually do that. I don't think this has any observable effect on battery life for me. However, enabling this in Sway results in some very odd behavior that breaks certain things so I've had to disable it. I can go into more detail on that if you like.
2) Hardware accelerated video decoding. In contrast to the fist one, this makes a HUGE difference in CPU usage and battery life. However this unfortunately cannot be used in any browser AT ALL in Linux, regardless of setup or configuration. The way I watch youtube videos on my laptop is usually with mpv, which does use hw decoding if it is configured to do so.
> enabling this in Sway results in some very odd behavior that breaks certain things
I've been using Firefox Nightly in Wayfire (also wlroots based) with GL (and even WebRender) for quite a long time now, it works very well, about the only issue left is popover placement is odd occasionally. What issues do you have?
With hw rendering enabled, opening a single Firefox window and browsing works fine. However when I try to open a new window the browser and desktop immediately become incredibly laggy and eventually unresponsive. I think I was able to successfully open a different tty and kill Firefox, which then fixed the issue, but it repro'd every time. Open one Firefox window, everythings fine. Open two, things slow to a crawl.
I'm surprised you were able to get WebRender working as well, I think I recall Firefox instantly crashing when I tried that. This was a few weeks ago.
If I disable HW acceleration on the desktop it's horrible perf wise, like VSCode and all the electron app are slow, there is aliasing all over the place when moving windows, slowness ect ...
( Ubuntu 18.04 / Unity on a Dell XPS 13 from 2016 )
1) HW accelerated rendering in Firefox, which despite being unfortunately disabled by default on linux can in my experience be enabled (on about:config) without issues. This makes the experience of scrolling much smoother, so I usually do that. I don't think this has any observable effect on battery life for me. However, enabling this in Sway results in some very odd behavior that breaks certain things so I've had to disable it. I can go into more detail on that if you like.
2) Hardware accelerated video decoding. In contrast to the fist one, this makes a HUGE difference in CPU usage and battery life. However this unfortunately cannot be used in any browser AT ALL in Linux, regardless of setup or configuration. The way I watch youtube videos on my laptop is usually with mpv, which does use hw decoding if it is configured to do so.