User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1 Safari/605.1.15

Steps to reproduce:

nothing special, just keeping Thunderbird open in background

Actual results:

fan started spinning loudly, and MacOs listed thunderbird as high battery usage application

Expected results:

the app should not be this cpu-intensive in idle

Hi Luigi, do you perhaps have your Preferences Tab open in TB when high idle CPU load occurs? We have localization bug 1642415 for that...

(In reply to Thomas D. (:thomas8) from comment #1)

Hi Luigi, do you perhaps have your Preferences Tab open in TB when high idle CPU load occurs? We have localization bug 1642415 for that...

Nope, just incoming mail tab opened.

Update: I noticed that high values of CPU/power usage occur only if I hide the window (clicking on the red x on top-left).
If I leave the incoming mail window opened on another Space the CPU values are normal.

Do you have a language pack installed?

(In reply to Wayne Mery (:wsmwk) from comment #4)

Do you have a language pack installed?

I use Thunderbird in Italian, and have both English and Italian dictionaries downloaded. Does that count as language pack? I don't remember downloading the Italian language pack, is it possible that thunderbird did it by itself?

Thanks. No, dictionaries are not language packs.

How much memory is being used by Thunderbird?

When the window is hidden the app uses more than 2GB (see the new files attached). When left open, the app uses about 200MB.

Memory usage when the window is hidden

Memory usage when the window is left open

Does problem go away after Help > Troubleshoot mode?
Do you have non-default cursor size set in Mac?

I have the default cursor size.
In troubleshoot mode the problem seems to go away. I will attach another screenshot showing memory usage.

Since it's only a problem when in the background, I suspect it's gloda (the global message index) that's using that time to do indexing/synchronization. You can turn it off in the preferences.

But gloda isn't a "background only" operation.

What percent of CPU is being used?
And does it go away after Help > Troubleshoot Mode?

As I said, the problem apparently goes away in troubleshoot mode.

Thunderbird uses about 5% to 10% of CPU while idling. If I hide the window, the CPU use drops to 0.1%, with brief spikes to about 4%.

Please create a performance profile and post the URL here.
Instructions at https://support.mozilla.org/en-US/kb/profiling-thunderbird-performance

Actually, I am having some trouble creating a performance profile: I cannot click on "Stop recording performance", so I guess the .json file is not completed, and I cannot upload it on profiler.firefox.com. I will attach the file here.

profiler file created by hiding thunderbird window

yes, profile.json is not complete. It fails to upload to https://profiler.firefox.com/

try running the profiler for a shorter period before clicking "stop"

I can't click stop even if I only let the profiler go for a second... what should I do?

(In reply to luigicatello16 from comment #22)

I can't click stop even if I only let the profiler go for a second... what should I do?

Does disabling global indexing in preferences help (per Magnus' suggestion). What are your results after doing that?