> Don't forget that Chrome users are more tech savvy on average than Firefox users
I somewhat doubt that. They're both mostly non-default browsers where they are used (and the places where Firefox is default probably have more technically savvy users than those where Chrome is default), Chrome has far and away more current mindshare and is, therefore, probably more likely to be a crowd-inspired (rather than technically-inspired) choice as a non-default browser. I suspect that there was a time when your statement was true, but I don't think its true now. (Though inertia in both camps may make it true even when its less likely to be true for new users.)
I don't doubt that Chrome has a lower (real or, even moreso, measured) CTR, I just doubt that its particularly because Chrome users are more tech savvy.
Tech savvy isn't the only explanation for CTR differences, especially measured CTR difference; ISTR a while ago discussions of what was possible in Chrome v. Firefox for adblocking, and from that it seemed that Chrome ad blockers would still download (but not show) ads, while Firefox wouldn't download them. Don't know if that understanding was accurate or if it is still the case, but that could conceivably result in Chrome impressions being overstated (and CTR being understated) relative to Firefox.
I somewhat doubt that. They're both mostly non-default browsers where they are used (and the places where Firefox is default probably have more technically savvy users than those where Chrome is default), Chrome has far and away more current mindshare and is, therefore, probably more likely to be a crowd-inspired (rather than technically-inspired) choice as a non-default browser. I suspect that there was a time when your statement was true, but I don't think its true now. (Though inertia in both camps may make it true even when its less likely to be true for new users.)