Hi ritamontague, do you use "Quit" to exit out of Firefox, either:

• "3-bar" menu button > Quit
• (menu bar) Firefox > Quit

If you use the X button, then Firefox would treat that window as a closed window and you would need to use one of the following to get it open again:

• "3-bar" menu button > Library > History > Recently Closed Windows
• Library toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

If Firefox doesn't remember either open or closed windows at your next startup, there could be a problem with settings.

Session history is considered part of browsing history, so it is important that not be cleared. More details if needed.

Thank you for responding. I quit Firefox via the Firefox tab. I looked and saw that I had "Delete Cookies and site data when Firefox is closed" checked. I unchecked it and was able to keep my tabs. It's unfortunate, because I would like to delete cookies but keep my tabs. I have a Mac so the three line menu bar doesn't show up. Anyway, I fixed it the best I could. Thanks again.

Thank you for the update. That particular setting shouldn't prevent restoring tabs -- I use that setting -- but maybe changing that setting changed something else at the same time. ??

As a backup to the built-in feature, you could consider a session management extension. These are the ones I'm aware of that you might investigate/try out:

Use database storage:

• https://addons.mozilla.org/firefox/addon/tab-session-manager/
• https://addons.mozilla.org/firefox/addon/session-boss/

Use bookmark storage:

• https://addons.mozilla.org/firefox/addon/session-sync/
• https://addons.mozilla.org/firefox/addon/my-sessions/

Thank you. I will keep those in mind. It's weird that it worked even when it shouldn't have, but I am happy about it.