For the technically minded what I did to fix the Firefox update problem was to remove the cookie named aus2.mozilla.org. (There are detailed instructions below about how to remove the aus2.mozilla.org cookie).

The error occurs after Mozilla Firefox attempts to perform an automatic update check, or when you select the menu option ‘Help’ -> ‘Check for Updates..’. The error is displayed below.

How to fix the error ‘AUS: Update XML File Malformed (200)’ and update Firefox

1. Open Firefox and choose the menu option ‘Tools’, and then select ‘Options…’

2. Click on the ‘Privacy’ tab, and then click on ‘Show Cookies’.

3. Scroll down the list of cookies until you find the ‘aus2.mozilla.org’ cookie (they are in alphabetical order). Click on ‘Remove Cookie’.

4. Check to see if the problem has been fixed by performing an update. Select the Firefox Help menu, then ‘Check for updates..’.

5. If the problem has not been resolved please visit the mozillaZine software update page , or the Firefox support website for more details about what may be causing the Firefox update problem on your computer.

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