Click on the row of bars on the upper right corner of the browser to bring up the menu.
Now, you will see Firefox’s Options menu. Select: Settings.
On the settings page, select Privacy & Security on the left-hand sidebar.
Scroll down until you see Permissions. Near the bottom of the permission options, you will see a checkbox next to Block
pop-up windows. Check this box to turn on the pop-up blocker or uncheck this box to turn off pop-up blocker.
Click on the row of bars in the upper right corner of the browser to bring up the menu.