hello dennis.guerra,

follow the steps:

• click 3 horizontal lines at the top of your window. Select "Options..."
• Click the "Tabs" icon at the top of the "Options" window.
• Click the check box next to "Open new windows in a new tab instead." Click the "OK" button at the bottom of the "Options" window to apply your new settings. Warning.

thank you !

The 3 horizontal lines does not offer "Options..." I selected "Preferences". In the "Tabs" section their is no "Open new windows in a new tab instead."

Hello agin dennis,

3 horizontal lines means manu bar which is top right on firefox screen.

But Firstly update your browser.

I think you have not latest version of Firefox

Please update your browser and follow my previous steps:

Update firefox:

Click the menu button ,

click. Help and select About Firefox. On the menu bar click the Firefox menu and select About Firefox.

The About Mozilla Firefox Firefox window opens. Firefox will check for updates and download them automatically.

When the download is complete, click Restart to update Firefox.

I hope resolved your problem then reply back to me.

Thank you and Regards,

Arman khan

You might be accidentally triggering the 'tear-off' feature to move the tab to a new window by slightly dragging the tab down if you click.

In Firefox 74 and newer there is a pref on the about:config page to disable tear-off and prevent moving the file accidentally to a new window.

• browser.tabs.allowTabDetach = false

There is still "Move Tab -> Move to New Window" in the Tab bar context menu to use this feature.
You can drag the tab back to the Tab bar in the original window to undo the 'tear off'.
Firefox will automatically close the now empty window.

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox