Open Firefox. Tap the Firefox app icon, which resembles an orange fox wrapped around a blue globe. Tap ☰. It is at the bottom of the screen. A pop-up menu will appear at the bottom of the screen. Tap Settings. This is the gear-shaped icon in the pop-up menu. If you do not see Settings, swipe from right to left across the pop-up menu. Tap the orange "Block Pop-up Windows" switch It will turn white Doing so will allow pop-ups in your Firefox browser app.