Right click that toolbar and select Customize. Is the missing button available in the dialog box that opens? If so drag and drop it back in place. I have never used that button so I cannot say for sure it is there.

Good suggestion, but unfortunately the "unread" option is not present in the customize panel.

Pete

Maybe you had an add on providing this button that needs upgrading to work with the new version.

Pressing the letter N on the keyboard is the shortcut for Next Unread until you figure out the button. It must have been an add on that created the button because I can find nothing showing it as a standard button in Thunderbird.

I found this add on that lists the Next Message button.

https://addons.mozilla.org/en-US/thunderbird/addon/toolbar-buttons/?src=search

Does this sound familiar? Is it showing in your add on tab in Thunderbird?

All of these responses got me looking at Add-Ons, and to my surprise I found that while I did not have the toolbar-buttons add-on, in fact *all* my existing add-ons were disabled. I'm fairly certain that I did not do this knowingly, but enabling them brought the desired button back. Thanks!

Pete