Log SSL-Connections:
To log SSL-connections for imap-sessions enter
# export NSPR_LOG_FILE=/tmp/mozlog.txt # export NSPR_LOG_MODULES=IMAP:5
and start mozilla.
Update: This does also work with thunderbird and firefox. See also Mozilla Wiki
Change user agent string:
In prefs.js:
user_pref("general.useragent.override", "my own useragent string");