Make it a habit and use File > Exit to close all open windows at once the prevent this. If you use the close X then you only close the current window.

ok what you sed is useful tested it and yes it works if i close the session from exit all instance and tabs are saved so as to avoid losing the main on. but chodent they do a history on the sessions , so that there wood be sonthing like a undo ore restore.... Thats just my opinion it wood be useful :P >>>lost my 40+ Tabs many times and with them the animes manga(losing the names and page) ore othere things i was doing :((((( <<<

Session restore works more reliable if you choose Tools > Options > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time" instead of relying on the Save & Quit dialog.

i have that option turned on fore a long time but its not really 100% relibel, im intrested if thers any way to prevent firefox from ever opening a new window ore pup-up, ore if it dose to ask fore my consent|(so i can avoid the problem all togheter), beause i never use more then one window at a time as navigating tabs is really easy. Btw thank you fore taking youre time to help me out

JediMobius has detailed the only way to get back a lost session. Firefox has backups - you just have to know where to find them. See: https://support.mozilla.org/en-US/questions/813545