OK, how old is the old version? What OS? WIndows?

Old version is 102.3.0 (64 bit). New version is 91.13.1 (32 bit) Operating system is Windows 10.

You cannot go from 102 to 91. I encourage upgrading the 91 to 102 and then it is very easy; ver 102 has the feature to transfer profiles built in. Tools>Export from one and Tools>Import from the other.

David I upgraded Ver 91 to 102. Now I have two versions running. One is 32 bit, the other is 64 bit. Seeing that my PC is 64 bit, I want to retain the 64 bit version. In Settings, I found two listings in Apps for Mozilla Thunderbird. One is (x64-en-US), the other is (X86 en-US). I assume I can delete the x86 version but I don't want to delete it before I am sure I am not deleting my version that holds all the data, files etc. What I can't understand is why I received what is apparently an old version of Thunderbird.

Start each separately. Then click help>moretroubleshootinginformation, scroll to profiles, click 'open folder' . Windows will show the exact location of the profile. write that down. Now, repeat the process for the other version of Thunderbird. Write that down also. Are they the same? Then both are using the same profile. If different, then you're safe to delete the ver 91 version profile. Regardless of that comparison, you would still be safe to remove the executables (confirm the location by right-clicking on desktop shortcut), but I would be hesitant to tell Windows to uninstall ver 91, for fear that the registry entries may be confused between the two. (Uninstalling may be safe, but I've never uninstalled a second copy, so I can't advise it.)

Hello rclloyd.

When looking at this post, I wonder if you have achieved what you wanted to achieve, that is transferring your data from one version of Thunderbird to the other? When looking at what you wrote, it kind of makes sense why you had what you had, so I'll try to make sense of it.

As you stated, you had an old or existing version of Thunderbird on your computer, which was the 64-bit version 102.3.0. Somehow, you got a new version which was the 32-bit version 91.13.1. Do you mind me asking how you got that since it makes no sense unless those version numbers would be reversed? I can see if you had the 32-bit version first and then manually downloaded the 64-bit version, or vice versa, but there does not appear to be a logical explanation of this being an automatic update at all, just because of the difference in bit type, 32 compared to 64. Either way, having different bit types would explain why you had more than one reference in your menu system.

Now as it has been explained to you, it would be best to open each version separately to see what each version contains. If the 102 version was your preexisting version, it would be safe to assume that all of your data would be within that version. But whether anything was transferred over to the "new" version, that being the 91 version, could only be found out by opening that version to see. As you would hopefully have taken note of the directories on your computer where the respective profiles are located, you could go to those locations and copy files from those locations and back them up to other locations.

As for your mail folders, if they are POP3 accounts, there should be directories and files on your computer in your respective profiles that correlate to them. They should be simple text files that you can copy to another location on your hard drive for back up purposes. Though they are simple text files, they are formatted for Thunderbird to read them. You would have two files for each "e-mail folder": a named file (i.e. Inbox) and an index file (i.e. Inbox.msf). And these files would be in a directory named for your account (i.e. pop.internet-provider.com). These would be located in a directory called "Mail", that would exist within your profile directory. If you have IMAP accounts, they would be a little different as the messages would be stored on the mail server and you just have a copy on your hard drive, whereas with POP3 accounts, you have the ONLY copy on your hard drive. So with POP3 accounts, you can just copy the entire directory that would be named for your account to another location on the hard drive for back up purposes, and any other local directories with e-mail files in them that you saved to a local location, like the "Local Folders" location in Thunderbird.

When you move these directories back into a new version of Thunderbird, you can remove the .msf files as they will/should be rebuilt when they are re-indexed. And you know that you should only move the files back when you do NOT have Thunderbird open, so it can be read properly. Also, if you have existing folders in your version of Thunderbird with the same names as your back ups, you may want to maybe change the name of the account directory, so it doesn't overwrite your existing folders. As an example, if your directory is pop.internet-provider.com, maybe renaming the directory to something like backup.internet-provider.com, so even that will be different from the original. Then afterwards, you can just either copy the respective e-mails over or move them from one folder to another, your back up to your existing copy.

Now as for things like your address book, you can load up the address book and then export it to a .csv format, which again should be a simple text file but in comma delimited format. After exporting it from one version, you can then import it to the new version that you want.

So whatever you decide, hopefully this information can give you a little more confidence to at least make a back up copy of your folders and address book(s) before you proceed, just in case you might need to wipe out both versions of Thunderbird and start anew. If that is the case, you can either go to Thunderbird's website and download the latest version or go to https://ftp.mozilla.org/pub/thunderbird/releases/ and download the appropriate release version that you want to have/use. So as I said, hopefully this was helpful and good luck to you.