I get 80mb for reddit on firefox.

That number can be down to any number of different factors on reddit itself. Having an autoplay video running, etc.

Memory measurements reported in browsers come with substantial caveats, as measuring "how much memory is this tab using" is fairly nontrivial.

Not saying there isn't a difference, but you'd need to measure (e.g.) a fresh install viewing only one tab with no extensions, etc.

I will eat the RAM penalty to resist the Chromium hegemon. Grateful to have any alternative!