I've set to "true" the <i>mail.compose.attach_http_images</i> preference. I've also unchecked the box "Send message as plain text if possible" and changed to "Send the message in HTML anyway" the drop-down box option under "When sending messages in HTML format . . ." Regardless, Thunderbird continues to block pasting images referencing operating system files into the compose window (displaying "Thunderbird has blocked a file from loading into this message. Unblocking the file will include it in your sent message."). Is there anyway to change this behavior? I've already studied:<br> • The explanation under "Mail composition" on this [https://support.mozilla.org/en-US/kb/new-thunderbird-52#w_mail-composition <i>New in Thunderbird 52.0</i> page]<br> •The release note mentioning <i>mail.compose.attach_http_images</i> on the page [https://www.thunderbird.net/en-US/thunderbird/52.0/releasenotes/ <i>Thunderbird Release Notes Version 52.0</i>] And these threads:<br> • [https://support.mozilla.org/en-US/questions/1172011 <i>Embedded images in TB 52.3.0 don't display when editing message</i>]<br> • [https://support.mozilla.org/en-US/questions/1183434 <i>Thunderbird fails to properly insert pasted images</i>]<br> • [https://support.mozilla.org/en-US/questions/1210374 <i>Since 2/23/18, cannot insert photo from file or copy/paste picture into email</i>]<br> • And these specific to the signature file: [https://support.mozilla.org/en-US/questions/1158319 <i>HTML signature file containing images, now blocked by Ver 52.0.1</i>] and [https://support.mozilla.org/en-US/questions/1118903 <i>Created a signature with an image. See it when I compose but recipient can't</i>]