Firefox includes a Software Update feature that automatically checks for updates and prompts you to install them when necessary.
Sometimes, the updater fails and displays an Update Failed error message. This article presents possible solutions and workarounds to get Firefox updated.
One solution is to update Firefox by manually downloading and installing the new version over top of your current version. See How to download and install Firefox on WindowsInstall Firefox on LinuxHow to download and install Firefox on Mac for instructions.
It's possible that another running program or a previous instance of Firefox that did not close properly is interfering with the Firefox update process. This error can also occur if you share your computer with other users, and another user's account is still logged in with Firefox running. The easiest way to resolve such problems is to restart your computer. Once the computer starts up again:
Some programs that can interfere with Firefox are set to start up automatically when you start your computer. Before updating Firefox, try closing or disabling such programs; for example, Spybot TeaTimer and Logitech QuickCam software have been known to interfere with Firefox updates.
If you are using Windows 7 or Vista:
If the issue is not resolved, close Firefox and restart the computer again but this time, open the program folder where Firefox is installed (e.g., open the C:\Program Files\Mozilla Firefox folder or, on 64-bit windows, the C:\Program Files (x86)\Mozilla Firefox folder), right-click on the firefox or firefox.exe file icon and select Run as Administrator.
Based on information from Software Update (mozillaZine KB)