I don't understand. You can exit thunderbird, and then download thunderbird, and then run the update that overlays existing version. but be sure to exit thunderbird first.

Hey David

Thank you for responding. Yes I did turn off Thunderbird prior to downloading the new reload. See attached error message, PLUS another issue I forgot to mention in the previous tickets. Your reply posted NINE (9) times. The while thing has gone wacky! Any ideas? Thanx Rob

Do you have an antivirus on your mac. I think you do, and it is what is out of control.

Several things seem to be going on here.

1. There have been problems with notifications lately. People are working on them. Let's hope for improvements.
2. You seem to have tried to respond to David's post by replying to the e-mail notification. That doesn't work. Click on "Post a reply" in the e-mail message.
3. You seem to be trying to open a disk image that was sent to you as an e-mail attachment, without first saving it on your drive. If it is the right disk image for your computer, try saving it to your drive, closing Thunderbird, and then opening the disk image. If you are not already using version 136.0, I would first try updating Thunderbird from Thunderbird settings - General. If you are not sure that the disk image that you have is the right one, go to https://www.thunderbird.net and download the program.

Per the last suggestion, I moved the dmg icon to my hard drive. It told me this updated version is not compatible with my old macOS 10.13.6 (High Sierra), which, unfortunately, is the highest I can go on my 2009 mac. I know there is a bogus way to over-ride that restriction, but don't have the tech skills to utilize it.

Also I turned off any auto scans for my virus program. Also no change. SO - is there a way to update repair the original

I believe that older versions of Thunderbird are available at thunderbird.net.

Sorry guys. I have followed all your suggestions yet not all issues have been resolved but Thank you all your time and consideration.

Tried again downloading the dmg for my old OS system directly from your site (not email) Version 115.18.0 (64-bit).dmg and still got the 'corrupted image error' message. I think I need to over-ride the entire old program to fix all the issues. Just a reminder, I still have the old macOS High Sierra, 10.13.6 on a 2009 iMac so I can't upgrade the OS. I either have to buy a newer iMac or find an alternate email system. Don't want to do either. Don't have the money to do the former.

Partial success: Turning off the "Startup Optimization" feature on one of my virus protection apps seems to have stopped the massive duplication of emails, but the Notification feature in the TB setting is still non-existent, so every email received is still popping up on my screen. Without access to the Notifications feature, I can't turn it off!

Ideas?

Again. Thank you all your time and consideration. Rob

What are you doing to trigger that corrupted image message? You are just double-clicking on the image in a Finder window or on your desktop, right? Do you have that anti-virus program completely disabled when you do that?

I am with Matt. This does not seem to be a Thunderbird or even a Mac issue. Something else such as an anti-virus program is interfering.

I have been an advanced, tech news following user of Macs since 1987. I have never known a reason to use anti-virus software on a Mac.

Please use https://support.mozilla.org/en-US/questions/1498480