Do you create the new window using, for example, the New Window menu item or the Ctrl+n keyboard shortcut? That will open with your home page(s) so it may be that you have multiple tabs set to open as your home page(s). If you don't want all those pages in each window, you can edit your home page setting on the Options page.

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the first section, under Home Page, check the box. Additional pages are separated by a vertical bar ("|") character, for example, this will open three tabs in every new window:

https://www.google.com/|https://www.yahoo.com/|https://www.mozilla.org/

Is that the problem?

That was not the problem..I'm sure it's something very simple..

I'm not 100% clear on whether you are opening a new window (Ctrl+n) or a new tab (Ctrl+t). Or if you are doing it a different way.

Is this a problem with the Windows Taskbar showing a thumbnail image for each tab instead of only one per window? To go back to one per window, it's this setting on the Options page:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Scroll down to the Tabs check and uncheck the box for "Show tab previews in the Windows taskbar".