Recovering address books from a damaged profile
In the unfortunate event that your profile is damaged, it is possible to recover your address books, even if the profile itself is unusable. Of course you have made regular backups which you can simply import, but just in case you hadn't... read on.
First, copy the damaged profile, or at least the ".mab" files, to a safe place. Next, you will have to make a new profile, configure your accounts and preferences, etc. Start Thunderbird and go to the address book. Create some new address books ("File -> New -> Address Book"). Create as many address books as you had in the damaged profile, and give them names like "AB1", "AB2", ...
Now exit Thunderbird, and go to the new profile folder. You will see files with names like "abook-1.mab", "abook-2.mab", with small file sizes, because they are empty. Copy the saved ".mab" files from the old, damaged profile into the new profile. For each ".mab" file from the old profile, there should be a file with the same name in the new profile. If there isn't, rename the old file, giving it the name of a new file which is not used yet.
Start Thunderbird again, and go to the address book. If all is well, the newly created address books are filled with the contents of the old ones. You can now change the names "AB1", "AB2", ... into something more meaningful by right-clicking on each address book and choosing "Properties".
Of course, if your old address books have been damaged, this procedure will not help.