Paul,

Have you resolved your problem?

I found out that Thunderbird stopped using .mab files and is using .sqlite files for addresses

Ended up manually recreating address book entries myself.

Not sure why going to a new format was not undertaken in the upgrade process but there you have it...

peace

Does your profile directory still have the .mab.bak files for the missing address books?

I checked both profiles in C:/Users/Username/AppData/Roaming/Thunderbird/Profiles and there were no xxxx/mab/bak files

That should have been :

I checked both profiles in C:/Users/Username/AppData/Roaming/Thunderbird/Profiles and there were no xxxx.mab. bak files