User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 Build ID: 20170330221232 Steps to reproduce: - Compose a mail via the plain text editor - Write some text - "Paste as quotation" some text - Cut all text and paste it again This is often done to re-order the contents of a mail, a quite common use case. Actual results: The quotation is not recognized anymore as a quotation. Sending as plain text with f=f inserts a leading space before the ">". (See also bug 1356012) Expected results: The text should be pasted with the same format as it was cut/copied, i.e. the quote should be recognized as a quote and rendered in blue.

Simpler STR: In a plaintext reply, or in a plaintext composition where "Paste As Quotation" was used, cut any quoted line and paste it again. It loses its "quote-ness", that is, its colour and the fact that no space stuffing of the > would have taken place. This is well known and well documented here: https://dxr.mozilla.org/mozilla-central/rev/c697e756f738ce37abc56f31bfbc48f55625d617/dom/base/nsDocumentEncoder.cpp#1356 (I wrote that comment, in fact). In a nutshell: When copy/pasting from a plain text composition, you have the choice between two evils: 1) Lose white-space 2) Lose formatting (colour, style, quote-ness, etc.) For TB we chose the latter, FF chose the former. Sadly the Core::Serializers module is unowned and no work is done there by Mozilla core staff.