If the shield button turns into a glove button, you know at a glance that a popup was suppressed. Hover your mouse over the glove button to see the URL of the suppressed popup.

For other annoyances, look at the color of the round button to the right of the slider:

Nothing was suppressed.

Something potentially annoying was detected, but nothing was suppressed. Click the button to find out what was detected.

Something was suppressed. It could have been a popup, or a window resize, or a timer, or any of the numerous annoyances; perhaps several. Click the button to find out exactly what was suppressed. Here are some typical responses.