unable to open more than 6 browser windows - Nicol

After 6 browser windows are opened, everytime i try to right click to "open
in new window", the 7th window doesn't appear. Sometimes the right click
doesn't even work. I can only close 1 existing window to open a new window.

This happens occasionally. Sometimes it works normally and I have no limit
to the number of windows I wish to open. Hope someone could assist me in this.