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 (There are detailed instructions below about how to remove the 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 ‘’ cookie (they are in alphabetical order). Click on ‘Remove Cookie’.

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

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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Adobe Reader 8.1 problem – AdobeUpdater.exe running at 100% CPU

I encountered a problem after updating Adobe Reader to version 8.1 where the AdobeUpdater.exe process would run at near to 100% CPU. I was unable to end the process in the Windows task manager despite repeated attempts.

The impression I received from reading about the experiences of other people with this problem is that is related to certain firewall software products not allowing AdobeUpdater to connect to the internet. Updating my firewall settings to allow this process full access to the internet did not resolve the problem.
If you are suffering from the AdobeUpdater process as well I can suggest four possible solutions:

  1. Review and update your firewall settings to allow the AdobeUpdater process to access the internet.
  2. Install an earlier version of Adobe Reader.
  3. Try installing alternative PDF viewer software such as FoxIt Reader.
  4. Prevent the AdobeUpdater process from running, detailed below.

Fix the AdobeUpdater problem – when you have Adobe Acrobat 8.1 (not the free version)

If you want to continue using Adobe Acrobat but have a problem with AdobeUpdater causing your computer to run slowly there is a work-around described here, as excerpted from the discussion on the Adobe forum here – AdobeUpdater.exe hogging all the CPU runtime (the solution is highlighted in bold text).

Hi Pam,

Sorry my message wasn’t clear, I copied it from another post.

What I did was to rename ‘Updater.api’ in C:\Program Files\Adobe\Acrobat 8.0\Acrobat\plug_ins to ‘Updater.api.PROBLEM‘ (subtle, eh?)

That way, Adobe can’t find the updater program to run it. I’ve had this fix in place since the 26th Feb and I’ve had no recurrence of the CPU problem and apparently no problems caused by my fix either.

Hope that helps.

Best regards,


Fix the AdobeUpdater problem – when you have Adobe Reader 8.1 (the free PDF reader)

If you are using Adobe Reader 8.1 (the free PDF reader) and you want to stop the AbobeUpdater process from running then the instructions are slightly different to if you are using Adobe Acrobat.

The following screenshots will show you how to rename the Updater.api file. These are taken from a computer running Windows XP.

Step 1 – Open the ‘Run…’ command.


Step 2 – Enter the following in the ‘Open:’ field :
C:\Program Files\Adobe\Reader 8.0\Reader\plug_ins


Step 3 – Right click on the Updater.api file, and select the Rename option.


Step 4 – Rename the file to Updater.api.PROBLEM and press the Enter key.


This big downside to this workaround is that you will miss out on notification of new releases and updates. It’s not a perfect solution but it’s the only I found that let me continue to use Adobe Acrobat 8.1.

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