Do you develop and test using Chrome, or Firefox, or both? If you aren't testing in Firefox beyond "it displays correctly" but you are using Chrome for your no

Do you develop and test using Chrome, or Firefox, or both? If you aren't testing in Firefox beyond "it displays correctly" but you are using Chrome for your normal development, and testing, you are de-facto optimizing for Chrome, because you'll notice slowness in Chrome and work around if, but that same thing may have been fast in Firefox, but you never noticed. That's what being the market leading browser grants them.