macos sierra close window closes tabs

[39Restorod]

With Firefox on my iMac, when I use the close window button to close Firefox and then restart it, all the open tabs from the previous session have been closed. If I quit Firefox and then restart it, the open tabs from the previous session are there. How do I get the close window action to function like the quit action (keep tabs open across sessions)?

[dfoulkes]

In case Mac works differently than Windows... you might want to include MAC into your topic title...

I use this extension for sessions...
Session Manager :: Add-ons for Firefox