Firefox won't start after windows update

Question

After windows Updated my computer Firefox won't start. I tried a clean reinstall two times, won't work. When I tried to start the firefox the first time after booting my computer it comes with the following message.
XML Parsing Error: undefined entity
Location: chrome://mozapps/content/extensions/update.xul
Line Number 14, Column 1:
<wizard id="updateWizard"
^
Any Help would be greatly appreciated. I like firefox and I'm using it the last 7 Years.
Thanks
DK

Answer 1

I cheated a little bit and put the issue url in a working version of firefox:
chrome://mozapps/content/extensions/update.xul
What I got was a page that looked like this below and console:
blah blah parser:
<pre><nowiki> xml-stylesheet
xml-stylesheet
<wizard id="updateWizard" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" title="Firefox Update" windowtype="Addons:Compatibility" branded="true" onload="gUpdateWizard.init();" onwizardfinish="gUpdateWizard.onWizardFinish();" onwizardcancel="return gUpdateWizard.onWizardCancel();" onclose="return gUpdateWizard.onWizardClose(event);" buttons="accept,cancel" pagestep="1" currentpageid="dummy" firstpage="true" lastpage="true">
<script type="application/javascript" src="chrome://mozapps/content/extensions/update.js"></script>
<stringbundleset id="updateSet">
<stringbundle id="brandStrings" src="chrome://branding/locale/brand.properties"></stringbundle>
<stringbundle id="updateStrings" src="chrome://mozapps/locale/extensions/update.properties"></stringbundle>
</stringbundleset>
<wizardpage id="dummy" pageid="dummy"></wizardpage>
<wizardpage id="offline" pageid="offline" next="versioninfo" label="Firefox is working offline" onpageadvanced="return gOfflinePage.onPageAdvanced();">
<description></description>
<checkbox id="toggleOffline" checked="true" label="Go online now." accesskey="G" oncommand="gOfflinePage.toggleOffline();"></checkbox>
</wizardpage>
<wizardpage id="versioninfo" pageid="versioninfo" next="mismatch" label="Checking Compatibility of Add-ons" onpageshow="gVersionInfoPage.onPageShow();">
<label>
Checking your add-ons for compatibility with this
</label>
<separator class="thin"></separator>
<progressmeter id="versioninfo.progress" mode="undetermined"></progressmeter>
<hbox align="center">
<image id="versioninfo.throbber" class="throbber"></image>
<label id="versioninfo.status" flex="1" crop="right"></label>
</hbox>
<separator></separator>
</wizardpage>
<wizardpage id="mismatch" pageid="mismatch" next="checking" label="Incompatible Add-ons" onpageshow="gMismatchPage.onPageShow();">
<label></label>
<separator class="thin"></separator>
<listbox id="mismatch.incompatible" flex="1"></listbox>
<separator class="thin"></separator>
<label>
Firefox can check if there are compatible versions…
</label>
</wizardpage>
<wizardpage id="checking" pageid="checking" next="noupdates" label="Checking for Compatible Add-ons" onpageshow="gUpdatePage.onPageShow();">
<label></label>
<separator class="thin"></separator>
<progressmeter id="checking.progress"></progressmeter>
<hbox align="center"></hbox>
</wizardpage>
<wizardpage id="noupdates" pageid="noupdates" label="No Compatible Add-ons Found" onpageshow="gNoUpdatesPage.onPageShow();">
<description></description>
<separator class="thin"></separator>
<hbox id="updateCheckErrorNotFound" class="alertBox" hidden="true" align="top"></hbox>
<separator class="thin"></separator>
<description id="noupdatesCheckEnabled" hidden="true"></description>
<vbox id="noupdatesCheckDisabled" hidden="true"></vbox>
<separator flex="1"></separator>
<label></label>
<separator class="thin"></separator>
</wizardpage>
</nowiki></pre>
I do not see much about coloum 14, but I am guessing this file is stored somewhere and its corrupt. Update.xul suggests that it is the update file. Do you still have this in your downloads folder? There are two places for update and for a clean reinstall:
[http://www.mozilla.org/en-US/firefox/new/] in a private window will give you a new install or you can choose from here: [https://www.mozilla.org/en-US/firefox/all/]
This is what the file should look like; [http://hg.mozilla.org/mozilla-central/log/7a2edc5171e6/toolkit/mozapps/extensions/content/update.xul] If you can copy and paste that file from a working browser we can see the issue, but it will just look the same as the error.
if you can replace the contents of the file locally with what it should look like it will fix the error, but who knows if there are other errors. May be best to delete the updater and save all the profile folder contents.