One of my app tabs for some reason opened in a new window; how do I get it back w/other app tabs on original window?

Question

I have 5 frequently-used websites on app tabs on my Firefox browser window. I've had these since I first saw the update about app tabs, and I have never before had a problem with it.
Today, I was working in one tab, and realized I needed to check something on the website at another app tab. I have done that sort of thing many times. But for some reason today, when I clicked on that other app tab, there seemed to be a long wait like it was working hard to make the switch, then suddenly a new Mozilla Firefox window opened with the only tab being the "another app tab" that I had clicked on.
That particular app tab is now missing from my original browser window.
I must've clicked something by accident or hit another key while I was clicking with the mouse on the app tab that I wanted to look at. I have no idea why it opened in its own window and disappeared from my app tabs on the original window.
How do I get that app tab back with the others on the original browser window? Is there any way other than simply starting over and re-pinning that site as an app tab?
If I have to re-pin it on the original window, is there a way to make that app tab the 1st in sequence the way it was before it opened in its own window? It is my most-commonly-used app tab, so I'd really like it to be the first in line, so to speak.
Thanks.
~KathrynI

Answer 1

Make sure that you do not drag a tab in the browser window.<br />
Firefox 3.5 versions and later have a feature called tear-off tabs.<br />
You can detach a tab from the current window and open it in a new window by dragging a tab in the browser window.<br />
You can drag that tab back to the tab bar in the original window to undo that detaching.<br />
bug489729 (Disable detach and tear off tab):
*https://addons.mozilla.org/firefox/addon/bug489729-disable-detach-and-t