I don't believe this is currently possible without an extension installed. Cookies and other data are linked to the website, not to a specific tab. That's why you can login on a website in one tab, but you can open that website is multiple other tabs without having to login each time.

If you are looking for a way to keep cookies contained only within a specific tab or group of tabs, the Multi-Account Containers feature is probably something worth looking into. Although, it still doesn't clear data when a tab is closed.

Before closing the tab, click on the padlock towards the left end of the urlbar and select "Clear cookies and site data...".

You can use these steps to keep cookies for websites you want to remember you and clear all other cookies.

• create a cookie allow exception with the proper protocol (https:// or http://) to make a website remember you

You can check that you aren't clearing important cookies.

• using "Delete cookies and site data when Firefox is closed" keeps cookies with an allow exception
• using "Clear history when Firefox closes" to clear cookies clears all cookies including cookies with an allow exception you may want to keep
• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exceptions for passwords and other website specific data

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Exceptions"

Don't use this to clear cookies unless you want to remove all cookies.

• Settings -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings

Thanks for the help everyone. Often times when I have 6 or so tabs open, and follow a link to something I want to read, it's just the tab I'm closing after reading that I'm concerned about. I DO have the "Delete cookies and site data when Firefox is closed" ticked in my preferences, but, I typically do NOT close FF. I think it's rather rare that I do actually!....unless I'm rebooting. I do go in and manage my cookies and trackers and have a bit of a delete party with them when I do. I think I'll work the "Clear cookies and site data" on the lock in the address bar for now for each tab I'm closing. I guess I was just wondering if there was a way FF could do that automatically when closing a tab. I'll check for an existing extension for this. Thanks again everyone!