Yet another Firefox update was released late yesterday. You can update your version by opening Firefox, clicking on Tools - then Check for Updates. Follow the prompts to finish the updated. Or, you can download 3.5.2 at www.mozilla.com.
People ask all the time - "Should I install the update when prompted?" Again, the answer is always "Yes". They are undoubtely fixing a security problem, a bug, or many of each!