IMAP logging doesn't work in TB

[Yuri]

Setting these two env variables as suggested in documentation here 
https://wiki.mozilla.org/MailNews:Logging only produces an empty 
/tmp/imap.log:

export NSPR_LOG_MODULES=imap:5
export NSPR_LOG_FILE=/tmp/imap.log

I was trying to troubleshoot this PR: 
https://bugzilla.mozilla.org/show_bug.cgi?id=666765 and found that 
logging isn't working.

FreeBSD-8.2-STABLE amd64
thunderbird-3.0.11

Yuri