The current workaround options in Thunderbird 91* are clunky but do achieve the right result. '''To get just highlighted text and no Subject:''' Highlight the selected text, open a new Write window and paste in the copied text. If you use an auto added signature you may want to edit to remove Then use the File > Print to open - you do not get the email headers and there is no Subject in the header section and all selected text is the only text shown in Print Preview. '''To get highlighted and a Subject in the top header.''' Highlight the selected text and use 'Reply' A new Write window opens showing only the selected text. If you use an auto added signature you may want to edit to remove and then use the File > Print to open the Print Preview window. As it is using 'Reply', you will get the usual 'On x date name of person wrote' You do get the RE: Subject in the header section and all selected text is the only text shown in Print Preview. Last option: Otherwise you could right click on email and use 'Edit as new message' and then edit all the unwanted text before using Print. There was a bug on this, but it's not looking like anyone is interested in fixing it. https://bugzilla.mozilla.org/show_bug.cgi?id=1731183 '''NOTE:''' Keep checking out this addon - PrintingTools NG 2.0.61 by Christopher Leidigh Message & Address Printing Tools (NextGen) New 78 Update with compatibility for 89 Note: NOT COMPATIBLE With 9X.X yet - working on it This addon is not compatible with version 91* as yet, but the author is currently working on it. The addon does mention 'Print selected text only', so it would be worth keeping an eye on this addon for when a compatible version is available. * https://addons.thunderbird.net/en-us/thunderbird/addon/printingtools-ng/

See https://support.mozilla.org/en-US/questions/1355197