What i don't get is that it's an unknown problem, many people have already filed bug reports on the tracker:
https://news.ycombinator.com/item?id=18626325
(also see several blog posts like: https://www.kamshin.com/2018/07/firefox-on-macos-insane-batt...)
I think it has to do with running the Macbook Pro at scaled resolution which is pretty much standard among devs on MB pro no? (otherwise you will have very little screen real estate).
I just created i Profile through the Gecko profiler once again but i don't know if that captures the CPU data? What external profiler do you use?
Profile here from Firefox nightly, 1 minute of scrolling around https://fs8.transfernow.net/download/5c0a9b99f98e/master/Fir...
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Very non scientific test below that i need to external profiler to confirm:
Symptoms:
I get a hot computer when browsing / working normally
high CPU usage leading to
fans constantly running and battery drain
Doesn't happen in other browsers
Comparative methodology:
Open 20 tabs and scroll a bit up and down for 1 minute.
Check CPU usage in Activity monitor.
Check fan speed an temp.
Repeat in all major browsers.
Result:
Safari, Chrome and Opera the fans stays silent and i get moderate CPU usage.
Firefox the fans kick in quickly (also ran first to have a fair baseline temperature).