You may have turned on 'Controlled folder access' in Win10. Check your notifications and make sure your browser is allowed.

Also see https://docs.microsoft.com/en-us/windows/security/threat-protection/microsoft-defender-atp/enable-controlled-folders

Even though you're trying to download the Thunderbird installer, most likely this isn't a Thunderbird problem.

But I don't have Win 10 - I'm using Windows 7. I've been using Thunderbird for a couple of years and this has never happened before. The only reason I know I had a new Thunderbird version yesterday because when I logged on I got a system message asking if Thunderbird was allowed to change the hard drive and I answered yes. This is the standard thing that happens every time there is a new Thunderbird version.

Oops, sorry - just realised I wrote Firefox when I meant Thunderbird. I've now edited the question. The file I downloaded is Thunderbird Setup 68.4.2. It just won't open. No error message.

I logged on I got a system message asking if Thunderbird was allowed to change the hard drive

This does not sound like a message you'd get when updating Thunderbird. Can you be a little more specific about that system message?

Thunderbird wouldn't open after update on 5 Feb.

What happens when you attempt to open Thunderbird? Is there any error message? Can you post a screenshot of the error?

Sorry, I can't be more specific about the message I get when Thunderbird updates. I've had it a handful of times and it seems to occur when there is a major update. I think the message is from Windows but it's possible it's from my anti-virus or firewall software. After the update on 5 Feb, the Thunderbird icon has disappeared and is replace by a generic icon. When I click on this icon I get the two messages in the screenshot attached to my first message.

So I tried downloading Thunderbird again. I got an application file but clicking on it does nothing - it does not open and there is no error message. Right-clicking gives you an option to run as administrator. I tried this and got an error message saying I do not have permission. There is also a troubleshoot compatibility option and running that seemed to indicate it's compatible with Windows XP, not Windows 7. Then I tried the Restore previous versions option, but there were no previous versions however there was a compatibility tab which allowed me to select Windows 7 in place of Win XP. I did this but it still wouldn't run. I've had a look on the Mozilla website and can't find any versions to download that specify Win 7, and I can't find anything on my computer that will allow me to revert to a previous version.

Is your Windows 7 computer 64 bit or 32 bit ?

The error message mentions :

• C:\Program Files\Mozilla Thunderbird\

not

• C:\Program Files (86)\Mozilla Thunderbird\

Did you download and install a Thunderbird windows64 bit version or a Thunderbird windows32bit version ?

Suggestion: Manually Access:

• C:\Program Files\Mozilla Thunderbird\
• delete the 'Mozilla Thunderbird' folder.
• Then empty the 'Recycle Bin'

Check this location:

• C:\Program Files (86)\Mozilla Thunderbird\
• If it exits and also has a 'Mozilla Thunderbird folder, then delete that 'Mozilla Thunderbird' folder as well.
• Then empty the 'Recycle Bin'

Access:

• https://www.thunderbird.net/en-US/thunderbird/all/

Download and install the 'windows32bit' (it's in black font) version for preferred language.

I had already downloaded the 32 bit version, however I followed your instructions and deleted C:\Program Files\Mozilla Thunderbird\. There was no C:\Program Files (86)\Mozilla Thunderbird\ folder. I downloaded the 32 bit version again - same thing, it just doesn't open.

It's probably time to get a new computer anyway rather than just buying Win 10 to install on this one, but I wanted to recover some of the emails which I now can't access. I found where the files are stored in Appdata\Roaming\Thunderbird on the hard drive and I copied files from Mail\Local Folders to ImapMail\Read in the hope that when I logged on to email on my ISP, the files would be there in the Read folder. But they weren't. I don't know if there are other programs that I can use to read emails stored in Thunderbird format?

re :I downloaded the 32 bit version again - same thing, it just doesn't open. Thunderbird is probably installed perfectly ok. Somehow, it looks like you do not permissions to run it, so need to set it up. C:\Program Files\Mozilla Thunderbird\thunderbird.exe You need permissions to run 'thunderbird.exe', so it the 'properties' of 'thunderbird.exe' where you should be looking. Please read the info at this link as it discusses how to fix the issue.

• https://support.microsoft.com/en-gb/help/2669244/windows-cannot-access-the-specified-device-path-or-file-error-when-you

re :I found where the files are stored in Appdata\Roaming\Thunderbird

Suggest you copy the 'Thunderbird' folder as it will have everything. This can then also be a backup.

re:I copied files from Mail\Local Folders to ImapMail\Read

No that will not work as you have discovered. When Thunderbird starts, it synchs with server and shows what is on server, so the files/emails you copied will be erased as they do not exist on server.

When Thunderbird is runnng, you can copy emails from 'Local Folders' folders into an imap folder of choice. Then the emails will get put back onto server. Suggest you do it in batches and always use the 'copy' not the 'move' option as it is less risky if something gets awry.

You may need to set permission or unblock the file etc. Check all the info supplied in that link I sent to you.

Thanks. I tried every one of those apart from disabling anti-virus. I have Avast and Malwarebytes and have updated previous versions of Thunderbird with them running. I had a quick look at both but couldn't find an obvious "off" button and didn't want to mess things up so left them. The other thing I changed, as I have tried previously, was in Compatibility where it showed Win XP and I changed it to Win 7. But I think you're right that it is a Windows problem rather than a Thunderbird problem. I may just have to wait till I buy a new computer, load Thunderbird on it and copy the files across.

Thanks for taking the time to help.

Try to start Windows in safe mode with networking enabled. - Win7 https://support.microsoft.com/en-us/help/17419/windows-7-advanced-startup-options-safe-mode#start-computer-safe-mode=windows-7

Does the problem go away?