If you see the error message, "Firefox.app can't be opened because the identity of the developer cannot be confirmed" when you try to open it, here are a few things to try.

Try this first:

  1. Hold down the Control key while clicking on the Firefox icon in the Dock or on the Firefox application file in a Finder window.
  2. Click Open in the context menu.
  3. Click Open in the following dialog window.

If that doesn't resolve the issue, try this next:

  1. Click on the Apple icon at the top left corner of your screen and open System Preferences.
  2. Click on Security & Privacy, then select the General tab.
  3. You will see a message stating that the Firefox.app was blocked. Click on Open Anyway.