[Bug 1908082] Re: Ubuntu Firefox is 15% slower than Flatpak Firefox for speedometer benchmark

[Tynach]

@osomon, I don't think this is due to the toolchain version used. I semi-recently (I don't know how long it's been going on.. Somewhere in the span of the last 6 months to the last 2 years? Probably more like the past year and a half, but it feels in some ways longer, in some ways shorter?) found that none of the shaders I've written on Shadertoy can run at 60fps. Not even relatively simple ones like this one:
https://www.shadertoy.com/view/MtGcRW

There's no reason for this to run at 40 - 55 fps, but it does. In fact,
no matter how simple I make a shader - even just showing a static
unchanging color - Firefox will never run it at 60fps.

This might have started when I upgraded to 20.04 from 18.04, but I'm
unsure.. I feel like I'd have remembered when it started better if it
was definitively after a major upgrade (I use Shadertoy frequently). I
do know I've tried using a blank profile, and also tried disabling all
add-ons and so on. I've tried using WebRender, having WebGL run in a
separate process, and all sorts of other tweaks via about:config.
Nothing gets any Shadertoy shaders to 60fps.

However, they all run at 60fps easily in the version downloaded from
Mozilla's website. What's more, is that I've been using Firefox instead
of Chrome for the past few years, and when I first switched over the
Ubuntu packages worked fine and ran shaders at full speed.

I remember that when I first noticed Firefox not running them at full
speed, I assumed it was Shadertoy's fault. Maybe they'd left some
debugging code enabled in the Javascript, and that was slowing it down.
So I just figured I'd ignore it and wait for it to be fixed by them.

After a month or two of waiting, and seeing the site actually update
with some minor changes here and there without it being fixed, I decided
to test Chrome. Ran fine. Tried all sorts of tweaks, nothing helped
Firefox run it faster. I still thought it was Shadertoy's code that
changed and was just not optimized for Firefox. Then a few months after
the problem started, I finally tried running a copy of Firefox from
Mozilla... And it ran just fine.

I don't know if that's the same problem as here, but this bug was
reported within the window of time when I remembered seeing the slowdown
(granted, that's a huge window due to my poor memory). And if it is,
then it can't possibly be only because of being compiled on an old
version of the compiler toolchain, as it used to run faster than it does
now.

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https://bugs.launchpad.net/bugs/1908082

Title:
  Ubuntu Firefox is 15% slower than Flatpak Firefox for speedometer
  benchmark

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