Sorry, the message didn't keep the formatting. Here are the files again, a bit more clearly: compreg.dat  ; extensions.rdf  ; local store.rdf  ; logins.json.corrupt [must be corrupt file - will it replace itself?]  ; mimeTypes.rdf  ; search.json  ; session_error_20161217104742672.json  ; TestPilotErrorLog.log.1  ; dxpti.dat

Most extracted from http://kb.mozillazine.org/Files_and_folders_in_the_profile_-_Thunderbird

compreg.dat Lists registered XPCOM components. Automatically regenerated whenever XPCOM registration process is triggered.

extensions.rdf Obsolete. Installed extension information. It can be deleted to remove "ghost" entries from the extension list [4] and to resolve various other issues.

localstore.rdf Obsolete. Replaced by xulstore.json in one of the updates to version 38. It stores the toolbar, window layout and size/position settings. It can be safely deleted to resolve various issues.

logins.json Stores encrypted passwords, and requires key3.db and cert8.db to work. Replaces signons.sqlite, which had replaced signons.txt

mimeTypes.rdf Action to perform when downloading certain types of files. Can be deleted to reset download actions.

search.json List of installed search engines. probably not a good candidate for deletion, but make a backup and if something does not work put it back.

session error wil be a log that can be deleted. Testpilot was killed of many versions ago so nothing there os an real use. from what I can see DXPTI.dat should recreate itself.

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Matt said

Most extracted from http://kb.mozillazine.org/Files_and_folders_in_the_profile_-_Thunderbird compreg.dat Lists registered XPCOM components. Automatically regenerated whenever XPCOM registration process is triggered. extensions.rdf Obsolete. Installed extension information. It can be deleted to remove "ghost" entries from the extension list [4] and to resolve various other issues. localstore.rdf Obsolete. Replaced by xulstore.json in one of the updates to version 38. It stores the toolbar, window layout and size/position settings. It can be safely deleted to resolve various issues. logins.json Stores encrypted passwords, and requires key3.db and cert8.db to work. Replaces signons.sqlite, which had replaced signons.txt mimeTypes.rdf Action to perform when downloading certain types of files. Can be deleted to reset download actions. search.json List of installed search engines. probably not a good candidate for deletion, but make a backup and if something does not work put it back. session error wil be a log that can be deleted. Testpilot was killed of many versions ago so nothing there os an real use. from what I can see DXPTI.dat should recreate itself. .

Hi Matt I hope that this reaches you (I don't understand how all of this works). Thank you so much for your help. Fantastic. Just not sure from the answer whether I can safely delete logins.json - whether it will replace itself. I have renamed it, though, to delete the word "corrupt". I don't ever store passwords on my computer, only trivial information such as login names. I have a version of that file from a previous backup in August 2015 - if I can't remove it, would it be safe to simply copy the old one into my present version of Thunderbird & delete the suspect one? Again, thanks so much. What a blessing to have people like you around. Leni, Adelaide.

just delete the logins file..... note that Thunderbird is about as safe a place to store passwords as you will find. Once you are storing passwords, enable the master password. This encrypts the password store making it unavailable unless the master password has been entered in the current session. So there is no accessing passwords while the program is closed.

THANKS AGAIN. I don't understand the technicalities but I've followed your instructions. Cheers. Happy New Year.

Matt said

just delete the logins file..... note that Thunderbird is about as safe a place to store passwords as you will find. Once you are storing passwords, enable the master password. This encrypts the password store making it unavailable unless the master password has been entered in the current session. So there is no accessing passwords while the program is closed.

THANKS AGAIN. I don't understand the technicalities but I've followed your instructions. Cheers. Happy New Year.