Make sure that you do not drag a tab slightly down in the browser window while clicking. Current Firefox versions have a feature called tear-off tabs. You can detach a tab from the current window and open it in a new window by dragging a tab in the browser window. You can also do this via the right-click context menu of a tab: Move to New Window You can drag that tab back to the tab bar in the original window to undo that detaching.

bug489729 (Disable detach and tear off tab):

• https://addons.mozilla.org/firefox/addon/bug489729-disable-detach-and-t

thanks

but the addon shows to be disabled by an administrator...

"This add-on has been disabled by an administrator. "

I'm old, just sometimes clicking around, when I click to highlight a tab, I guess my arthritis moves the mouse a hair...

Do you mean that you can't open the Add-ons web page via the link I posted above?

The link I posted above works for me, so the extension is still available.

My bad. Instead of clicking on install button near top of your linked page, I scrolled down on that page and clicked on this link:

If you want to undo detach and tear off tab, try "Undo Detach Tab" extension (https://addons.mozilla.org/en-US/firefox/addon/12689/).

Got the addon installed and it works great!

Thank you