A very old HTML signature block with my former company name is occasionally applied to outgoing emails instead of the default specified in Thunderbird How can I find and delete it? FWIW, I went to Tools | Account and I find the current proper signature block is there. So I don't know where Thunderbird is dredging up the old signature block from. I do have the Signature Switch plugin activated, but I've made sure that old signature block isn't in there. Any help will be appreciated: this is embarrassing when it happens and I send the email without noticing the bad signature.