What is the shield icon in the browser toolbar?

This is the Ad Blocker Site Reputation shield. It shows a site’s reputation — whether safe, possibly unsafe, or compromised — warning you about known malicious sites before you click into them.

When you navigate to a website, Ad Blocker will check the site you are visiting against an up- to-date list of unsafe sites kept in sync on your device. If the site you are attempting to visit is on the list, Ad Blocker will deem it unsafe. The Site Reputation shield will turn red and you will see a warning screen. You can choose to go back and stop navigation or proceed to the site anyway.

If the site is not on the list, the Site Reputation shield will be green. When you are on an empty tab, the icon will be gray. If the shield is amber, this is a warning that the extension has not been able to retrieve the Site Reputation list recently.

Note: If you are using Ad Blocker in Safari, you'll receive a warning screen on unsafe sites, but the shield will remain blue.