Funnily enough Chromium actually consumes less RAM and is safer due to better sandboxing.

But neither of these concern the average user. However, the main difference between the browsers user may notice is how pages that are still loading behave. Firefox has the correct behavior. Aka waiting for vast majority of the elements to finish loading versus Chromium just going "if it's rendered it's intractable." This unfortunately means that Firefox feels slower even though it's actually faster.

Also, on behalf of the dark mode enjoyers, flashing white for a moment while launching, loading web pages or updating contents of a webpage is incredibly annoying. None of the Chromium browsers flash white on dark mode.