Moving curser across page, without pressing button, window will close or open up another window.
Occasionally, when I am moving my cursor across a web page, it will either close or will open another window. It is as if I am clicking on the X to close the page or clicking on some other part of the page and it opens. When this happens, I do not have any buttons on the mouse pushed. It has been suggested that Norton is an issue, but I don't see how it could be.
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.