topic Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina in Discussions

Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

BlengBlong — Thu, 17 Jul 2025 02:46:56 GMT

Hi everyone,

I recently updated Thunderbird to version 140.0.1esr (64-bit) on my MacBook Pro running macOS Catalina, and I've encountered a serious performance issue since the update.

Issue Summary:

After launching Thunderbird, my MacBook's fans ramp up aggressively, and the CPU temperature spikes to nearly 100°C.
According to Activity Monitor, Thunderbird is consistently using around 60% of CPU resources, even when idle.
This behavior was not present in the previous version—Thunderbird used minimal CPU and ran quietly.

🧪 Troubleshooting Steps Taken:

Restarted the system and relaunched Thunderbird — issue persists.
Disabled unnecessary add-ons and extensions — no improvement.
Checked for background indexing or sync activity — nothing unusual.
Verified that no other apps are contributing to the spike — Thunderbird is the sole culprit.

📌 System Details:

macOS Catalina 10.15.x
MacBook Pro (15-inch, Mid 2012)
Thunderbird 140.0.1esr (64-bit)

Has anyone else experienced similar overheating or CPU spikes after this update? I'd appreciate any insights, workarounds, or confirmation from others facing the same issue.

Thanks in advance!

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

siffemcon — Thu, 17 Jul 2025 03:12:53 GMT

Lots of troubleshooting steps here.

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

aasawchuk — Fri, 18 Jul 2025 17:19:14 GMT

I noticed exactly the same behavior on my MacBook Pro (16-inch, 2019) running Catalina 10.15.7 and Thunderbird 140.0.1esr . The fans run continuously. Thunderbird uses 5% of CPU with nothing else but Finder active.

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

siffemcon — Sat, 19 Jul 2025 02:17:21 GMT

Did you try any of the troubleshooting steps I mentioned above?

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

aasawchuk — Sat, 19 Jul 2025 20:31:41 GMT

I completely solved the problem by going back and re-installing Thunderbird 128.11.1esr on my MacBook Pro running Catalina 10.15.7. No more overheating, no more continuous fan running. Thunderbird 140.0.1esr needs a fix.

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

andreamoretti — Thu, 21 Aug 2025 10:14:07 GMT

Hi everybody,
I have almost the same exact problem: MacBookPro9,2, Catalina 10.15.x, Thunderbird 140.2.0esr.
Almost because I have a difference: I always have two processes of Thunderbird running when Thunderbird is open, and the sum of CPU usage is always minimum 100%.

Thank you for the help

Andrea Moretti

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

siffemcon — Thu, 21 Aug 2025 21:38:13 GMT

The bug that causes this has been fixed but will take some time to appear on release versions.

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

wsm — Thu, 02 Oct 2025 17:20:40 GMT

I believe the issue with Catalina versions has been resolved in ESR version 140, currently 140.3.1. Let us know if is not.

Please in the future use https://support.mozilla.org/en-US/questions/thunderbird for support and problem issues. Thanks.

Re: Thunderbird 140.0.1esr (64-bit) Causing High CPU Usage and Overheating on macOS Catalina

andreamoretti — Fri, 03 Oct 2025 07:36:39 GMT

Yes, I confirm.

Thank you!