As someone that uses firefox and chrome I don't understand what you mean by "slower". What benchmark are you using to compare the two?
I haven't run specialized benchmarks, but in my case anything that has to do with playing videos is way slower in Firefox than other Chromium-based browsers (Chrome, Brave, etc.). In Firefox the video is not as smooth and skipping, especially when I'm not focused on that particular tab. I'm not sure if it has to do with GPU acceleration not working properly in Firefox for some reason. I have to check. Is Firefox playing videos (e.g. YouTube) as smooth as Chrome for you?
I've just installed it. Had to uninstall enterprise chrome (msi version) 1st but everything is working well.
Why? The only things I had to customize again were the "theme", "show bookmark bar" and "ask where to download files everytime" settings. Everything else including history, passwords, saved bookmarks, installed extensions and chrome profiles were recognized.
Dunno what settings or configuration or connection quality you have set up but I don't have any problems watching youtube through firefox. You might want to start a thread to get to the root cause of the issue.