As far as I know there is no possibility to Detach or Delete (nor Ccompress) inline (embedded) attachments (images) in Thunderbird.
For now, the only options (right click) on inline images are "Copy Image" and "Save Image As..".
Please add "Detach embedded Image" and "Delete embedded Image" (and may be "Compress embedded Image").
And also "Detach all embedded Images"...
Thanks a lot,
Bob