How to fix the Mozilla Firefox update error – AUS: Update XML File Malformed (200)

I was unable to update Mozilla Firefox because the error ‘AUS: Update XML File Malformed (200)’ was displayed. Below are the steps I followed to fix the Firefox update error – without having to re-install Firefox. Please note that the error message ‘AUS: Update XML File Malformed (200)’ is used to to describe more than one type of problem, so unfortunately the fix below may not work for you.

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.

Firefox Update AUS: Update XML File Malformed 200 error

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…’

Firefox Update AUS: Update XML File Malformed 200 error - choose tools->options

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

Firefox Update AUS: Update XML File Malformed 200 error - choose 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’.

Firefox Update AUS: Update XML File Malformed 200 error - remove AUS2.Mozilla.org cookie

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

Firefox Update AUS: Update XML File Malformed 200 error - 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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