edit menu > options (might be preferences on a mac.) attachments > incoming tab.

Remove whatever is there for a PNG. then try and open one again and select the correct application.

Kindly read what I wrote in my question: QUOTE However, the tools menu on my TB does not contain a Option and Attachment link Using: Thunderbird 52.9.1 Macbook Pro High Sierra UNQUOTE

I found however a solution: AA: close TB, BB: open the profile, CC: Find the file "mimeTypes.rdf" (on OS X the file is located like this: file:///Users/XXXXXX/Library/Thunderbird/Profiles/xyzaa86b.default/mimeTypes.rdf ) DD: Delete the file "mimeTypes.rdf" EE: restart the Apple computer or laptop: Problem solved.

If you know what you are doing, the you can open /mimeTypes.rdf in a text editor. Delete ALL the sections which mention the extension which create problems (in my case the .png extension) save the profile and start up again. (I assume you have made a back-up of the profile for safety reasons)

Best regards, Arne

Kindly read what Matt wrote.

edit menu > options (might be preferences on a mac.) attachments > incoming tab.

The word Tools does not appear anywhere.

The menus are different for Windows, MAC and Linux. For your review. http://kb.mozillazine.org/Menu_differences_in_Windows%2C_Linux%2C_and_Mac

Above answer from AirmAIL says "CHOSEN SOLUTION" This is an error, Airtmail did not supply an solution to my problem Kindly check my second note.

Arne said

Above answer from AirmAIL says "CHOSEN SOLUTION" This is an error, Airtmail did not supply an solution to my problem Kindly check my second note.

you "solution" is about as hard a way to do it and the most likely to cause failure of anything you could have done.

Unfortunately I gave you Linux menus, but really as you choose to use an operating system that less than 10% of people use you would do well to familiarize yourself with this menu map so everything you read does not confuse you. http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac

My understand of the difference is that Mac users expect to find options called preferences in the application menu (Thunderbird, firefox etc). Given that logic though I can not help but wonder why Mac users have so much trouble locating preferences, if it is located in the special apple location..

@Matt, I am sorry, but I need to remind you that this forum is made for people who have a problem, they are them helped by a lot of good people who knows what they are talking about. This is not a discussion club, specially comment like yours, which clearly indicate you do not know what you are talking about, should be avoided. as well as this is not a place to discuss about one operating system vs others. the official solution suggested by Mozilla is as I mentioned: close TB, Open Profile and delete mimeTypes.rdf and start up again.

Unfortunately, regardless of your assertions to the contrary, I feel I have no option but to undo your "solution". I do not want that turning up in a Google search leading folk to do rash things.

The correct approach is to fix the details for that file type in the options dialog of the application. That you can not find it does not make wholesale deletion of all mimetype handlers the correct way to do it. If the file were corrupt it might be a good idea to rename it. but deleting files is never a good way to solve problems.

While in this case it might work there will be disruption for every attachment opened while all the files types are relearned. Deleting was something that was done ten years ago when there were no user interface tools to manage the handling of mimetypes.

On an OSX system you would click the Thunderbird menu, select preferences then the attachments tab.

Just so you know.

• Mozillazine is an independent group. It is not associated formally with either Mozilla or the Thunderbird council that develops Thunderbird. I assume it is this article you got your information from. http://kb.mozillazine.org/Actions_for_attachment_file_types
• Mozilla do not develop Thunderbird, it is an independent community project.
• Mozilla do allow us the use of their support forum and knowledge base for supporting Thunderbird. But none of the content is provided by Mozilla.
• I have searched the entire knowledge base for a support article that mentions mimetypes.rdf. I can find only this one https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data