What is Firefox? Mozilla took Netscape stripped it to bare components and made them better. Why not do that again? Take Chromium, strip it to bare components and make them better.
We need a hard fork of Chromium today or it will happen in the future anyway.
Call it Google Social. Get the usernames from Gmail. Contribute to Mastodon like their are doing on Chromium or do a fork. Get the same policy and terms from YouTube. What can be that hard?
You want a Pixel 5 or 6a. Set smallest width to 432dp from developer settings. Check the result with mydevice.io to see 2.5x pixel ratio. You got a iPhone Max resolution for the size of a Mini.
The problem with color emoji is that they aren't affected by CSS color value. If you want to turn black to gray in an emoji, you have to use CSS opacity. Then you will trigger a different algorithm to render text containing emoji in all browser engines.