On a Mac you can close the window and open a new window to achieve that. That won't close the Firefox application. You can also right a tab and choose "Close Other Tabs" from the right-click context menu.

Set the pref browser.tabs.closeWindowWithLastTab to false on the about:config page to prevent closing the last tab from closing the browser and make a close button appear if only one tab is open.

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold(user set).
• Preferences can be reset to the default or changed via the right-click context menu.

Very much appreciate your good info. and quick response, thank you.

You're welcome