How do you close that tab?

If you use the close X on the title bar then you close the window.
If you have the tab bar on top then you may not see that easily.
You can close an individual tab with a middle click on that tab if that tab doesn't have a close button.

Thanks for the quick response Cor-el.

Here is exactly what I do:

1) I open AOL in a new tab in a current FF window. 2) I click on the "mail" link. 3) I click on a specific email to open it, which opens a new window. 4) When I finish reading the email, I close that mail's window, which closes out my whole session in FF.

I am confused bc it is a separate window, which should not affect the entire session...

How do you close that window?

I click on the X to close out of that email. It never did this before and it seems it's only with AOL. When the email opens, it opens in a separate window... Thanks

It's still happening... Anyone?

You haven't confirmed which close X you are clicking.
If that is the close X on the right side of the title bar then that closes the window.
To close a tab you need to click the close X on that tab or middle-click that tab or press Ctrl+W

Sorry if I wasn't clear:)

I have multiple tabs open, one of them being AOL. I click on an email to open it--the email opens in a new window, all while the other window with the tabs are still open behind it. When I finish reading the email (in that separate window), it closes out both browser windows,including the one with the open tabs and the separate window that has the email in it.