Checking for mail in all folders with mozilla-thunderbird.
Yay, it took a little, and why this is not an option somewhere in the options panel, I don’t know. To check for mail in all IMAP folders, add the following to ~/.mozilla-thunderbird/default/<random crap>/prefs.js
// Check for new mail in ALL imap folders
user_pref("mail.check_all_imap_folders_for_new", true);
(Thanks to whoevers’ blog I found that it. I’ve lost the link already.)