I think I got some sort of corruption in my Thunderbird address book file (
abook.mab). I had identical symptoms described in this post, namely the error message "Unable to load addres book file abook.mab. It may be read-only, or locked by another application. Please try again later."
So I renamed the file and it fixed the problem, but I noticed that the original
abook.mab was ~131Mb (larger than the mailboxes themselves). The address book (which seemingly could still be read even though it was complaining about something being wrong in the file) only had about 20 entries.
My question is: What can cause such a massive address book file, and is it anything to worry about?