hat exactly does that mean? It does not remember your choice to allow content from an address?, a particular site? or allow remote content for everything?

Thunderbird seemed to forget my choice to allow remote content from the address that sent an email. The result was that Thunderbird blocked remote content in the email.

Thank you for your response. I took it as a challenge to take a fresh look at the problem. The problem turned out to be caused by a program (CCleaner) that removes unwanted files from Windows and various applications. I had begun running the program weekly to clean Firefox cache. I had also never changed the default configuration in CCleaner for Thunderbird. Two particular options (Session and Site Preferences) acted together to cause the problem.

I would have thought after all these years the ccleaner folk would have learned they are deleting setting files in Thunderbird. I hope you have communicated with them in a stern manner that they are not supposed to be deleting your settings.

It is at least 8 years since I first became aware of the destructive nature of ccLeaner, they have released a lot of new versions over that time frame. On this forum their name is spelled MUD