Is it possible that once when you quit Thunderbird you had left open an email account in a second Thunderbird window? This might explain the second window on startup since Thunderbird automatically proceeds to a session restore: on next start it opens the same windows which were open at the end of the last session when you quit. To get rid of the superfluous window simply close it before leaving Thunderbird

Im not sure what was happening but the opening of windows on Thunderbird are back to normal, only opening one window at start-up..As far as having a second window open, I had checked beforehand and only one window was open..very odd indeed..thank you kindly.

Jesse A.

In whatever version of Thunderbird was current a year ago, I often experienced a strange problem. Thunderbird opened a window behind the one that I was using. I forget what triggered it. I may have been navigating to account settings. If I recall correctly, it happened sometimes even when I was just moving the mouse pointer, but I'm no longer sure of that.

It happened less over time. I have not seen it happen in several months now, I think, except maybe once. I downgraded to 140 esr about a month ago. I have not see it happen since then.

So, I can only guess that this problem could be related to the version of Thunderbird that you are using.