My girlfriend has now gotten an undesired option turned on and can’t figure out what invoked it or how to turn it off:
Some messages in the Inbox now appear with what looks like a cartoon balloon off to the left of the message, which now has a tiny icon with either a + or a - sign in it; clicking on the + causes a related message (threaded somehow?) to appear, indented, below it, with a dashed line connecting the two.
She wants to go back to just showing all the emails in the inbox in consecutive order, each on its own line, with no threading.
I’m not a Thunderbird user (I use Eudora) and I’m a Mac person, and so far I’m not much help here.