How to disable stripping signatures in plain-text replies?

Thunderbird automatically recognizes text after a single line consisting of two dashes as a signature. When replying via plain text to an email that contains such a signature, Thunderbird strips it off the quotation, including the dashes. I consider this an anti-feature for several reasons: 1. The stripped citation looks bad because it ends with an empty line prefixed by a > sign. 2. I'd like the citation to preserve the original mail as close as possible unless I choose to cite only parts of the text. 3. This kind of signature detection is fundamentally flawed - an earlier quoted mail might follow after the signature which is then also stripped. 4. It is inconsistent because it does not happen when replying via HTML mail. How do I disable this behaviour? Ideally I'd also like to disable the different coloring of signatures in plain text mails.