Firefox can't be opened after you install it on a Mac - How to fix

Revision Information
  • Revision id: 76902
  • Created:
  • Creator: flod
  • Comment: Minor nits. Note that on OS X in Italian it's always "Firefox", not "Firefox.app"
  • Reviewed: No
  • Ready for localization: No
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Revision Content
This issue applies to Mac devices only.

Apple has introduced a security change to Mac OS X 10.9.5 which causes the error message Firefox.app cannot be opened because the identity of the developer cannot be confirmed to appear when you try to install Firefox on your Mac.

Here are some steps you can take if you see this message:

Option 1 - Recommended

  1. Hold down the Control key while clicking on the Firefox file.
  2. Click Open in the context menu.
  3. Click Open in the following dialog window.

Option 2 - Open Firefox through the System Preferences

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