User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.1 Safari/605.1.15

Steps to reproduce:

I am the author of 6502.ts, a Typescript emulator for the Atari 2600. With Firefox 83, I experience a massive performance regression by roughly a factor of two if warp is enabled. I am afraid that I cannot provide more clues at what is driving the performance loss.

In order to reproduce the issue:

• Go to https://6502ts.github.io/stellerator-ng
• Import the attached ROM file by clicking on "Add New" (upper right corner)
• Start the game by clicking "Run"
• Remove the speed limit by deselecting "Limit Framerate" in the upper right corner
• Observe the speed of the emulated system in the upper right corner of the screen

Actual results:

With warp disabled in about:config, the game runs at about 9-10 MHz on my system. With warp enabled, the game runs at 4.5 MHz.

I have observed the same speed loss on other systems, so I am pretty sure that it is not connected to my system.

Expected results:

Speed should be equal or improved.

I checked and get the same result with Firefox 84.0b8

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Iain, can you investigate this speed difference?

Profile with latest Nightly: https://share.firefox.dev/3SzhNgZ (emulation speed is 7.2-7.7GHZ)
Chrome runs at 18MHZ emulation speed.