Firefox restores a window session from before the last time I closed the browser

Firefox restores a window session from before the last time I closed the browser every time I start the browser.

At one point after reinstalling firefox I had two windows open with tabs in each. I closed the one window first with a couple worthless tabs in it before using the other tab that I'd used to continue browsing and continuing my various tab groups. Ever since then, EVERY TIME I launch firefox it launches that other window with its tabs first, although allows me to "restore previous session" overwriting all but the base tab. How the hell do I get it to fucking stop doing this? I just want the last window I closed to be the "previous session" but every single damn time it launches this unwanted window and tabs as the default! I've tried countless times to close the entire browser with the window I want but it still reverts to the previous window!