The following is advise on how to use an old backup to completely reinstall the entire Thunderbird backup and also info on how to copy paste the default address books. Thunderbird has two default address books, in version 68*, they are called 'abook.mab' and 'history.mab'. As of version 78*, those files were formated into 'abook.sqlite' and 'history.sqlite'. As of 91*, I believe there was further updates to parts of address book although the names are unchanged. Those two default address books will automatically be referenced in the 'prefs.js' file of any profile name folder. It is possible to copy and paste those files from one profile to another, but to move any other address book, you have to copy/paste the entire profile or import previously exported address books which were saved as LDIF or .csv files OR if using version 91* you can import MORK *.mab files. '''If you want to try to import an old 'abook.mab' file:''' * Copy that backup 'abook.mab' file to desktop and then rename it to eg: oldpab.mab so the mab file name is different from the default name. * Tools > Address Book - to open the 'Address Book' * Tools > Import * select 'Address Books' and click on 'Next' * select Mork database (.mab) and click on 'Next' * locate and select the renamed 'oldpab.mab' file on desktop * click on 'Open' * click on 'Finish' I now see an address book called 'oldpab' in the list and when selected I can see contacts. On verision 91.3.2 I've just tested the import of mab file which I know is 5 years old. It was successful. '''IF you wanted to try and just get copy of 'abook.sqlite' and 'history.sqlite' into the current profile:''' Access profile name folder. * Menu app icon > Help > More Troubleshooting Information * Under 'Application Basics' - half way down 'Profile Folder' - click on 'Open Folder' * A new window opens showing you the contents of the default profile name folder. Note: 'profile name' folder is typically called something like this: abc123ew.default * Exit Thunderbird now. The 'profile name' folder will contain 'abook.sqlite' and 'history.sqlite' files. * As a precaution - rename the current 'abook.sqlite' and 'history.sqlite' files as 'abook.sqlite.bak' and 'history.sqlite.bak', so you still have them intact but not used. * Get copies of the backup 'abook.sqlite' and 'history.sqlite' files from the backup 'profile name' folder and paste them into the current 'profile name' folder. You can only copy across those two files. You cannot copy paste any other eg: abook-1.sqlite. * Start Thunderbird to see if you get access to those address books. '''If you want to try to get the entire backup up and running again with a fresh install:''' Since version 68*, Thunderbird has used a dedicated profile for each version. This means upon each update, there may have been changes to files, so that it is not so easy to downgrade, although it is possible. If you need to use an old profile, it is advisable to try to use the same version of Thunderbird which that backup was using and then update to next version until you are up to date. This means those files which underwent new formatting will get altered in a more gradual way. Uninstall current Thunderbird program. '''How to find out what version your backup copy was using at the time of backup:''' Access the backup profile name folder. In the 'profile name' folder, there should be a 'compatibility.ini' file which can be opened using a simple text editor program like Notepad. It will contain information like this: * [Compatibility] * LastVersion='''78.14.0'''_20210901192859/20210901192859 * LastOSABI=WINNT_x86-msvc * LastPlatformDir=C:\Program Files (x86)\Mozilla Thunderbird * LastAppDir=C:\Program Files (x86)\Mozilla Thunderbird In the example above, it used Windows 64 bit version 78.14.0 and the language was English British. So you would download that version from: * http://ftp.mozilla.org/pub/thunderbird/releases/78.14.0/win64/en-GB/ the file you download is 'Thunderbird Setup 78.14.0.exe' Then run it to install. The first time Thunderbird runs it would create a default profile. Do not add any mail accounts, just exit Thunderbird. Go to backup 'Roaming' folder: C:\\Users\username\Appdata\'Roaming'\'''Thunderbird'''\ Copy the 'Thunderbird' folder. On computer : * Exit Thunderbird if it is running. * Access the current username\Appdata\'Roaming' folder: * C:\\Users\username\Appdata\Roaming\'''Thunderbird''' * Delete the current 'Thunderbird' folder. * Paste the copied 'Thunderbird' backup folder into the 'Roaming' folder * Start Thunderbird. check all is ok before updating.

Thanks for your help. Importing the mab files didn't work. Copying the sqlite files did.