What you describe is freezing, not crashes. So there won't be any crash reports. How do you quit TB when it is frozen? Do you use the force-quit feature of thee Finder or via the Activity Monitor? Do you run antivirus software on your Mac?

Otherwise run the first test: launch Thunderbird in "Troubleshoot Mode" https://mzl.la/3AbU5jz Hold the Alt ⌥ key and launch Thunderbird...

If TB reproduces the same issue, make a test in a new Thunderbird profile https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles#w_start-the-profile-manager-when-thunderbird-is-closed

Thank you for the reply and the clarification. After posting my question here, I decided, for a laugh, to ask ChatGPT, which suggested that I disable notification popups for new messages in Thunderbird's configuration editor:

In the Config Editor, search "mail.biff.show_alert" and set its value to "false"

This solution worked. It was also the first time that I have ever had a coherent and non-hallucinatory response to anything in ChatGPT.

My only guess is that there was some conflict between MacOS and Thunderbird's apparently incompatible notification systems.

I decided, for a laugh, to ask ChatGPT, which suggested that I disable notification popups for new messages in Thunderbird's configuration editor. This solution worked.

I can't believe that the ChatGPT solution such as you report it was successful. That's why I really would like to read "in texto" the manipulation proposed by ChatGPT! Thunderbird's config editor does not manage the "banners" which popup in the upper right corner of the TB main window when a new message arrives. These are dependant on the user's choices in macOS System Preferences > Notifications > Thunderbird (see screen shot)

My only guess is that there was some conflict between MacOS and Thunderbird's apparently incompatible notification systems.

I've been using TB since the beginning on my successive Mac computers, always with those banners activated and without any incompatibility.

The only actual conflict I know between Thunderbird and recent macOS versions is that the integration of the macOS Address book is not working https://bugzilla.mozilla.org/show_bug.cgi?id=1720257#c55

I've been using TB since the beginning on my successive Mac computers, always with those banners activated and without any incompatibility. The only actual conflict I know between Thunderbird and recent macOS versions is that the integration of the macOS Address book is not working https://bugzilla.mozilla.org/show_bug.cgi?id=1720257#c55

I don't know what to tell you. Last Friday was the first time in my life that I've ever touched an Apple computer. My new MacBook Pro M4 was a complete virgin. So far I've installed a handful of programs, including Thunderbird, and have made no modifications to any system settings.

All I can tell you is that the little white box only appeared when a new message arrived, and then the white box wouldn't go away. If I closed the main Thunderbird window, it would not reopen under any circumstance, but the white box remained, with the truncated menu that only showed the Apple logo and "Thunderbird". I'd have to click the Thunderbird menu and quit in order to access the program and my e-mail.

In any case, the problem was quite clearly related to a conflict in new message notifications, by the fact that: 1) It happened only when the first new message came in after starting Thunderbird 2) The problem did not go away when I turned off notifications for Thunderbird through the Mac system settings (as seen in your screen shot) 3) It stopped happening only when I set display message notifications to false in Thunderbird's configuration editor

More than the above, I can't comment on, since I am a Mac newbie.

Fortunately, I don't use a Mac address book, so one less bug to face.

I found the ChatGPT instruction. Of course, it first advised me to turn off notifications in the Mac system settings. When that didn't work, it told me to open Thunderbird's Config Editor, then:

In the Config Editor, search "mail.biff.show_alert" and set its value to "false"

That worked!

When that didn't work, it told me to open Thunderbird's Config Editor, then: In the Config Editor, search "mail.biff.show_alert" and set its value to "false"

Thank you very much! Very clever this ChatGPT "guy". Sooner or later forums will die from AI. As a matter or fact now I remember those mail.biff.... preferences in the config editor. But I never saw a Mac screen like yours with Thunderbird in the upper left corner but without its tool bar!

Just to give you an idea of my Thunderbird "new message notification" in the upper right corner I add a screen shot.

LOL. ChatGPT didn't tell you how to solve the problem. It told you how to avoid it by making Thunderbird not create notifications…

I had to enable (set to true) that mail.biff.show_alert setting to make Thunderbird notifications appear on Mac OS, because I wasn't getting the notifications after upgrading both the OS and Thunderbird at some point, and couldn't figure why until I found that setting.

PS: I know it's currently called "macOS", but got eventually tired of Apple keeping changing how it is supposed to be written, so I always refer to it as "Mac OS" regardless of the version. It's their problem if they want to write it differently now… :P

LOL. ChatGPT didn't tell you how to solve the problem. It told you how to avoid it by making Thunderbird not create notifications…

Whether it solved or avoided the problem, I was impressed that ChatGPT came up with the answer in seconds that I was unable to find from hours of searches and trawling through forums like this one.

Fortunately for me, I find the notifications annoying, so preventing them solved two problems at once. Still, I found it offputting that a new computer and a new, current install of Thunderbird would result in an annoying bug. I was nervous enough about using an Apple product after 37 years of using DOS and Windows, so this issue raised a chill feeling of helplessness and regret.

OK, but software bugs happen. Trying Thunderbird Troubleshoot Mode, as Mapenzi suggested, might help to identify the problem if you ever want to investigate this further.