I should add that I have searched the entire C: drive for files matching the names of some received email attachments, to no avail. And when I open an attachment and investigate its properties, there is no folder location listed, which makes me suspect the file is still on the google server. Of course I can elect to save a given attachment to the local hard drive, but I would like all attachments to download to the PC automatically, as they used to. Cheers, Bryan

Perhaps you misunderstand the whole attachment thing.

Attachments are not files. They are blocks of mime encoded text in the body of the email and this is how Thunderbird stores them in the original email as mime encoded text. The folder you have set is to be the default when you select the save action in the attachment pane of an email. Nothing more.

If a folder is marked for offline use (the default) then the entire email and any attachments is stored on the local machine in the profile folder. If however you have set Thunderbird to not store emails on the local machine then they will be fetched from the gmail server as you access them. There is a cache that reduces this constant fetching a bit if you go back to the same email over and over. But for speed it is preferable to simply have a copy of everything locally.