I can not reproduce with windows 10 and Thunderbird 68.2.2.

Perhaps try the following to see if the source might be third party software;

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Matt Thanks for taking the time to answer! Starting Thunderbird in safe mode - same problem. Starting in Windows safe mode with networking - Works as expected.

I recently got the 1909 update, perhaps some Windows component? The File Explorer search "looks" different to what it was.

Any way to get Thunderbird to produce a crash dump file? Ivan

more likely a third party software. Usually an anti virus or an internet security suite as they now like to refer to them selves. What are you using?

I can confirm the Search works in the Select Image file window in TB 68.3 32b/W10 1909. Windows Defender is the only security app, with the TB profile folder added as an exclusion.

I have Windows Defender and Premium paid version of Malwarebytes. As both have ween running from long before the problem occurred, should I still suspect either of them to be the culprit?

With Malwarebytes turned off, problem still persists. I run Thunderbird version 60.9.1 (32bit version) in 64 bit Windows. I can update to later version of Thunderbird and report back. Thanks for the help so far.

Upgraded to TB Version 68.3.0 (64 bit) Problem gone, although the search takes much longer than it used to. Many thanks for your help and support.

Ivan said

I have Windows Defender and Premium paid version of Malwarebytes. As both have been running from long before the problem occurred, should I still suspect either of them to be the culprit?

Over the course of frequent updates for TB, WD and MB, there's bound to be a point where an incompatibility causes issues in TB, but if you exclude the profile folder from any security app (keeping the real-time background scan in place), you probably won't have any problems.

I may have to revisit. This problem is not completely solved. I had a case where I had to insert 2 images into an email. The first one worked as expected but the second not. Clicking on the search box did not crash Thunderbird but it stopped working. I knew the file name so could find it by typing into the "File Name" box at the bottom of the form.

This could be a Windows 10 issue? How can we determine?

I'm able to insert consecutive images using the Search without any problems. Did you exclude the TB profile folder in WD and Malwarebytes? Does inserting 2 or more images cause a crash when you run in Windows safe mode?