open your profile folder. There is alink in Troubleshooting information on the help menu.

Close Thunderbird. delete handlers.json (new) and mimetypes.rdf (replaced) and restart Thunderbird.

all settings for attachment handling will be reverted to defaults, but my guess is your time machine business has restored old setting that have not been migrated properly.

First, thanks for your quick and thoughtful reply!

I tried your method, but Tbird did not recreate these two files after restart, so there were no file types and no default applications in Preferences/Attachments. Same behavior when clicking on an attachment.

Interestingly, an HTTP association was created when I clicked on the link in the email sent from this forum. That association works, and it caused the creation handlers.json, but NOT mimetypes.rdf.

Any other ideas?

First, thanks for your quick and thoughtful reply!

I tried your method, but Tbird did not recreate these two files after restart, so there were no file types and no default applications in Preferences/Attachments. Same behavior when clicking on an attachment.

Interestingly, an HTTP association was created when I clicked on the link in the email sent from this forum. That association works, and it caused the creation handlers.json, but NOT mimetypes.rdf.

Any other ideas?

The mimeTypes file is obsolete and is replaced by handlers.json. The latter will be empty until you open an attachment and specify a helper app to open the file. If you check the box 'Always ... for this file type', the setting is added to handlers.json.

When you set the helper app, don't pick from the list presented, but click Browse... and select the app directly.

This makes sense. However,

> open an attachment and specify a helper app to open the file.

I am not prompted to associate a helper app when pressing the eyeglass icon. After I press it and nothing happens, the icon turns gray. This happens with multiple attachment types.

There are a few ways to open an attachment: select the file in the attachment pane and right-click, Open, or click the drop-down at the right end of the pane, Open, or press Enter. Do you not see a prompt to set the opening application, as in the attached picture? This is on Windows, but it may work differently on Mojave.

> Select the file in the attachment pane and right-click, On the Mac, the file appears next to the magnifying glass icon. Nothing happens when I click on the file, or when I right click on the file and select "open attachment.' Same when I use the "classic reader" format.

> Do you not see a prompt to set the opening application Nope. Nothing pops up.

Thanks for all of the great ideas so far.

To repair, I was thinking of uninstalling Tbird and reinstalling. Good idea? Also, I'm a little freaked out about losing my mail store, or having to associate a new install with the old, existing identity.

Uninstalling and reinstalling TB won't affect your data, which is in the separate profile folder, as long as you install the same version, 60.9, which can be downloaded here. But first, run TB in safe mode (hold Option when you launch TB, or Help/Restart with Add-ons disabled) and see if you can open attachments.

No difference with Safe Mode. Click on attached file or get menu and select "open" and still, nothing happens.

If I remove and reinstall TB, how do I point to the old, existing profile folder within: Users⁩ ▸ ⁨<myname> ▸ ⁨Library⁩ ▸ ⁨Thunderbird⁩ ▸ ⁨Profiles⁩

Thanks,

Robert

When you reinstall TB and run it, it will read the profiles.ini file in the Thunderbird directory and open with your existing profile.