On a MAC I think it is under Preferences-Attachments-Incoming In Windows it is Options-Attachments-Incoming

Thanks Airmail, but I found that it's set to ask me where to save it, not automatically save it to the desktop. However, I changed the save to location and, although it has the same problem, it now automatically saves it to the new location. So, this looks like a bug; it seems to always save the file even though the ask me where to save it button is selected. Oh, well.

a file has to be created and save to open. In windows that is placed in the temp folder. Does you mac have a temp environment variable set? perhaps it is defaulting because it can not find the temp folder.

Thanks, Matt. That was the clue I needed. I don't know if anyone else is having this problem, but here is how I set it up on a Mac running OS X 10.11 . . . 1) In the Finder, open the Go pull down menu. 2) Select Go To Folder at the bottom. 3) A window will open up. Enter /private and hit the Go button. 4) Find the folder called tmp, and make an alias of it. 5) Move the alias to your desktop. 6) Go to any location you like (I went to Library/Applications) and create a folder. I called my folder Thunderbird Temp Space. 7) Place the tmp alias in that folder. 8) Open Thunderbird's Preferences and select Attachments. 9) At the bottom of the attachments window, select the Save Files To button, and then hit the Choose button to tell it where to save the files. 10) Find and select the tmp alias you created. You will now notice that the window next to Save Files To says /private/tmp.

Now when you open attachments, they will open in the tmp folder. The contents of this tmp folder is cleared on each reboot.

tmpc said

Thanks, Matt. That was the clue I needed. I don't know if anyone else is having this problem, but here is how I set it up on a Mac running OS X 10.11 . . . 1) In the Finder, open the Go pull down menu. 2) Select Go To Folder at the bottom. 3) A window will open up. Enter /private and hit the Go button. 4) Find the folder called tmp, and make an alias of it. 5) Move the alias to your desktop. 6) Go to any location you like (I went to Library/Applications) and create a folder. I called my folder Thunderbird Temp Space. 7) Place the tmp alias in that folder. 8) Open Thunderbird's Preferences and select Attachments. 9) At the bottom of the attachments window, select the Save Files To button, and then hit the Choose button to tell it where to save the files. 10) Find and select the tmp alias you created. You will now notice that the window next to Save Files To says /private/tmp. Now when you open attachments, they will open in the tmp folder. The contents of this tmp folder is cleared on each reboot.

Could you please file a bug for this https://bugzilla.mozilla.org/ It may be that there is already something. I do not follow OSX bug very carefully. But the question you raise has been cropping up on fora for years and really I have no idea of the real cause. what you have demonstrates might provide some clue to making a Thunderbird fix for the issue, or documenting why and how to fix.

It is now in Bugzilla.

Thanks again, Matt.

tmpc said

It is now in Bugzilla. Thanks again, Matt.

Can you post a link... I like to follow along when I ask folk to report bugs, just to see they do not get a quick flick by Someone trying to tidy up, or telling you it is a support issue.

Geez, I'm not sure how to do that. I find the Bugzilla site to be quite confusing. The bug number is 1387292 if that helps.