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Tools | Options | Advanced | Config editor
user.js:
user_pref("mail.check_all_imap_folders_for_new", true);
user_pref("mail.imap.expunge_after_delete", true);
user_pref("mail.password_protect_local_cache", true);
user_pref("alerts.totalOpenTime", 4000);
user_pref("extensions.enigmail.addHeaders” , false);
user_pref("general.useragent.override", "");
Usefull plugins:
