Firefox Update Error - AUS: Update XML File Malformed (200)

Martin Brinkmann
Feb 3, 2008
Updated • Feb 5, 2015

The Firefox error AUS: Update XML File Malformed (200) is a general update error message that can not be attributed to one specific issue.

Generally speaking, the error has to do with either the offline mode, proxy servers, network connections or https. Those options are but a few of the possibilities but common ones.

I'd like to provide you with information on how I fixed the issue on my version of Firefox which threw the error one day.

You can of course check all the settings mentioned above which will probably lead to the setting or element that causes the error AUS: Update XML File Malformed (200) to appear.

I would propose two options instead which update Firefox without having to uncover the cause of the error message at all.

The first that comes to my mind is simply download the newest version of Firefox from Mozilla and install it over the old version. This updates Firefox to the latest version.

Another possibility - if you want to use the Update Checker - is to create a new profile in Firefox and use that profile to update Firefox.

The second method won't work all the time depending on the cause of the error message but it can help if the error is caused by options, extensions or settings of the current Firefox profile.

To create a new profile under Windows for Firefox you need to close Firefox completely and start it with the parameter Firefox -p which will open the profile manager on start.

Once displayed, click on Create Profile and uncheck don't ask at startup. Start Firefox and select the new profile and use it to update the browser.

It is usually a good idea to have a second profile configured in the browser for situations where you need to troubleshoot issues that you are experiencing while using the main profile.

Anyway, the manual download and update update should work regardless of that.


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  1. Tricia said on May 14, 2010 at 6:38 pm

    This did not help me but I will share what did work

    Check your Firewall settings it may be set to block everything without asking you first.

    Also try to look at the log to see what it has blocked and what programs are listed as trusted and be sure to add it as a trusted program if you can.

    Just by disabling it for 5 minutes showed me that’s where the problem was it was not my pc where mine are configured properly so it did not even cross my mind when I was trying to help my Dad that the problem was the firewall.

  2. booger said on August 23, 2009 at 8:03 pm

    Going to Tools/Options/Privacy/Show Cookies and deleting any and all cookies containing “Mozilla” usually works for me.

    1. Kenny said on January 26, 2010 at 9:08 pm

      Thanks, deleting mozilla cookies did the trick.

  3. atep said on July 18, 2009 at 7:42 pm

    hate to ask such a simple question, but how do i access my firefox profile folder?

  4. wecaz said on July 16, 2009 at 10:56 pm

    “renaming/deleting of file cert8.db in the folder of my firefox profile fixed this update problem”

    Worked like a charm !!

  5. George said on July 14, 2009 at 6:15 pm

    renaming/deleting of file cert8.db in the folder of my firefox profile fixed this update problem

    This worked for me as well.

  6. Hetti said on June 16, 2009 at 8:55 pm


    renaming/deleting of file cert8.db in the folder of my firefox profile fixed this update problem.

    Best regards

  7. Bren Flibig said on April 10, 2008 at 8:37 pm

    Well, it’s a hack all right.

    “I would propose two methods instead which update Firefox without having to find the error message first.”

    That’s about as hackish as you can get. Most of us would prefer to find and fix the CAUSE of the error, so any OTHER errors caused by the same problem will ALSO go away. In general, a reliable computer doesn’t HAVE unexplained, ignored error messages.

    “This are only a few of the possibilities and I would like to explain what you can do to fix this issue…You can of course check everything mentioned above”

    Well, no you can’t. You just said there’s a large number of possibilities, you listed only a few, and said nothing about how to find OR fix any of them.

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