Thunderbird has begun to shut down (not exactly a crash, since I get no error message; it just shuts down) when I'm composing a message. At the point where it would be saving a draft in the midst of composition, it tells me it wasn't able to save a draft. Then, whether I choose "try again" or "don't save," it will immediately shut down. Sometimes, though, I am able to complete the message and send it successfully; but about half the time, the program disappears and my partially-composed message with it. I'm using version 91.2.1, 64-bit.