Hello khoopes, how often is that ? do you have it soon enough , like one time in ten clicks on a tab ? can you check it in safe mode ?

Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

thank you

Are you using a mouse to click on the tab and do you move the mouse a bit while clicking? That can register as a drag, and it will cause the tab to become a new window. You can get the tab back into the original window by dragging the icon in the address bar onto the tab bar. I use trackballs and since I lift my fingers off the ball when clicking buttons, the cursor does not move when I click.

Make sure that you do not drag a tab in the browser window.
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 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