Separate Issue; Your System Details shows;

Installed Plug-ins

Adobe PDF Plug-In For Firefox and Netscape 11.0.15

Shockwave Flash 21.0 r0 Shockwave Flash 18.0 r0

Security Issue: Update your Adobe Reader Version 2015.016.20039 Note: Other Software is offered in the download.
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version: 21.0.0.242 Flash Player (Linux) Version 11.2.202.621

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download.

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download.

Did you do anything to create the new window? Were you opening a link at the time?

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
• Drag Tab as Shortcut: https://addons.mozilla.org/firefox/addon/drag-tab-as-shortcut/