Updates have been released in the past couple days for both Apple QuickTime and Mozilla Firefox. Both Mac and Windows computers are affected by both updates. If you have Apple iTunes installed, QuickTime was installed with it.
To make sure Firefox is up-to-date, go to the Help menu and select Check for Updates...
For information about the QuickTime patches and how to update (courtesy of US CERT):
- About the security content of the QuickTime 7.3 Update: http://docs.info.apple.com/article.html?artnum=306896
- How to tell if Software Update for Windows is working correctly when no updates are available: http://docs.info.apple.com/article.html?artnum=304263
- Apple QuickTime Download: http://www.apple.com/quicktime/download/
- Mac OS X: Updating your software: http://docs.info.apple.com/article.html?artnum=106704