Firefox works fine. It's my daily browser on a fairly old Macbook. No issues whatsoever, other than some websites that weren't tested on it.

People seem to think I'm crazy in my other comments when I said I often run into websites that don't test Firefox and thus do not work properly.

there are some observations of mine:

- when the browser is not in the visible workspace, chromium's cpu usage actually goes to 0 whilst firefox's usually oscilates around 5%

- every new window costs 30mb of ram for chromium and 100mb for firefox

- this one is weird, but when lightly using firefox while overall ram usage spilled well into swap, often after some time terminal emulator process will get swapped-out as if firefox eventually touched memory used by every tab sitting in the background

That's a fascinating bit of sleuthing! 1.5 watts is a substantial amount of energy when you're in the 4 to 5 watt overall usage range. You're not crazy and nitpicking.