I highly doubt this is the case. I can't tell the difference between my gaming desktop and my laptop with integrated graphics.
From what I've seen on the chromium bug tracker, Google has been on a ~5 year crusade to improve Mac performance. Around half the issues Ive seen include something like "We don't know what Mac does here, let's ask some people at the next conference" (these were core rendering performance bugs). I totally get why Firefox can't compete with that. It's fast on the platforms that don't seem to be hell-bent on making custom rendering slow.
From what I've seen on the chromium bug tracker, Google has been on a ~5 year crusade to improve Mac performance. Around half the issues Ive seen include something like "We don't know what Mac does here, let's ask some people at the next conference" (these were core rendering performance bugs). I totally get why Firefox can't compete with that. It's fast on the platforms that don't seem to be hell-bent on making custom rendering slow.