Those appear to be options to set in your Web browser, which is effectively the platform that LiChess runs on. You don't mention which browser you're using…
Chrome uses multiple cores and thereby searches many more nodes per second, without any special attention.
On my Mac, Firefox uses only one core, even after entering the settings you mention (using about:config). Chrome uses multiple cores and thereby searches many more nodes per second However, without any special attentionthe Linux version responds well to these settings.
Obviously, a native chess engine would be more efficient still. This wouldn't integrate with LiChess, however.