Works smoothly in Firefox. But the default key mapping is busted: fire at Alt means that it opens and closes the menu in Firefox with each press. Also, Alt + left arrow ends the game and goes back in history.
Interestingly, it was more choppy in Chromium.
I could not find a key for moving sideways ("strafing").
Firefox's WebRender is truly a great creation. While Chrome is faster at most things especially involving JS, Firefox puts so much of its rendering on the GPU so moving elements around is incredibly fast.
Strafing is implemented on A and D at least, but having one hand on the arrows to turn and WASD to move is a bizarre mix of modern and original controls
Interestingly, it was more choppy in Chromium.
I could not find a key for moving sideways ("strafing").
All in all, quite mind-boggling.