This article describes why you can get AUS: Update XML File Malformed (200) when Firefox checks for updates.

Table Of Contents

• Interfering extension
• Firefox can't access secure sites
• Incorrect update URL setting
• Cookies - Incorrectly set or Cannot be set
• Upgrading manually

Interfering extension

Disable any extensions that may be blocking access to the update server, such as Noscript. For more information, see Troubleshooting extensions and themes.

Firefox can't access secure sites

Firefox uses secure sites when it checks for updates. Make sure your Firefox is able to access secure sites without errors or prompts.

1. From the menu at the top of the Firefox windowbar, select FileFirefox and then select the ExitQuit FirefoxQuit menu item.
2. Start Firefox.
3. In the Location Bar, type https://addons.mozilla.org and press EnterReturn.

• If you get an error loading the site, see Error loading web sites.
• If you get a prompt for your master password or for a proxy password, then Firefox is not able to check for updates until you receive that prompt and enter the correct password. As a workaround, you can periodically check for updates manually after you've entered your password.

Incorrect update URL setting

Firefox may be set to use an incorrect address when checking for updates.

1. In the Location bar, type about:config and press EnterReturn.
   • The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!, to continue to the about:config page.
2. Search for the preference app.update.url.
3. Right-clickHold down the Ctrl key while you click app.update.url and click Reset.
   • If Reset is disabled, Firefox is already set to use the correct update address, so this isn't your problem.

Now that Firefox is configured with the correct address, it may be able to update without error.

Cookies - Incorrectly set or Cannot be set

Firefox may not be able to set or read cookies when it checks for updates. Make sure your Firefox is able set or access cookies, especially when using Stealther and/or other Privacy and Security add-ons.

1. Temporarily disable Stealther and/or other Privacy and Security add-ons.
2. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select Options...Preferences....
3. Select the Privacy panel.
4. Click the Show Cookies... button to open the Cookies window.
5. Find a cookie beginning with the name aus2. If it exists, select the site and click Remove Cookie(s).
   
   
   

Upgrading manually

If nothing else works, you can always download the latest version of Firefox from http://www.getfirefox.com and install it over top of your existing version. You won't lose your bookmarks or other settings. To prevent the error dialog from coming up, you can turn off automatic updates.