User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36

Steps to reproduce:

I'm the developer of a realtime multiplayer browser game and people have been reporting a lot of lag lately on Firefox.

I created a small test script to test the ping and found out that the results are a lot worse on Firefox compared to Chrome when I run it side by side.
All I'm doing in the test is run a server on localhost which sends performance.now() to the client, the client will send this back to the server, the server calculates the difference and sends that to the client again so that the client can output it.

Here you can see the code I used for testing, I've attached a screenshot with the results.
https://github.com/Rojoss/websocket-ping-test

I ran the test on a clean install of Firefox in a private window, no extensions and such.
The websocket protocol version is rfc-6455 for both Chrome and Firefox.
Firefox version: 95.0.2 (64-bit)
Chrome version: Version 96.0.4664.110 (Official Build) (64-bit)

Actual results:

The ping on Firefox is super high and increases over time even when the window is focused. There are also way more spikes in the ping.

Expected results:

The ping should be similar to Chrome and not increase over time.