If your desire is to work offline with the messages, these steps should do it: ' - click account settings>synchronization&storage and click the advanced tab to verify that the desired folders can be downloaded - then, click file>offline>download - then, click file>offlline>work offline

Hi David, thank you. This sound simple, but even still, I have not located the 'synchronization/storage' category under settings. When I am in my email account (mozilla) this is not a path I can find.

Copy the desired mail to a subfolder of Local Folders.

If I understand your suggestion, it means that the Local Folders is actually not a cloud/server storage but is on my PC?

Sfhowes suggestion is for a permanent move, whereas mine is assuming a desire for offline work. If you want a permanent fix, please follow Sfhowes' suggestion. On mine, click the hamburgermenu in upper right, then click account settings, not server settings. and then you will see the synchronization&storage under your account. We're both trying to assist, and not sure of your intent.