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

[BlengBlong]

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!

[siffemcon]

Lots of troubleshooting steps here. 

[aasawchuk]

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.

[siffemcon]

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

[aasawchuk]

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.