Running those four browsers at once is not a clever way to compare them. You should turn off all background process unnecessary for the operating system to work and then run just one browser, reboot each time you’re done with measurements. And to make sure whether the e performance depends on the operating system, you should do the same on every major OSes (Linux, MacOS and Windows). Don’t forget to open the same websites with the same number of tabs for a fair comparison.
Seems daunting? Stop comparing them, shut up and use Librewolf