Because Firefox doesn't offer any extra security controls over Chromium, in fact I would say they are way worse than vanilla Chromium on Arch. Therefore it makes sense to go with the browser that performs well, rather than one consuming a bunch of resources unnecessarily.
what security controls are you referring to? Also, I think we were talking about performance. How is performance relevant to security controls? And again, how does that imply that Mozilla is better/not better than Google?
I'm referring to the security controls that Mozilla and their Apple-like fan group claims give it an advantage over Chromium. I am saying that I do not believe that it has any security or privacy advantage to Chromium, and the performance is worse, so there is no reason to be in the Mozilla cult-like fan club.