diff --git a/packages/firefox-config.xml b/packages/firefox-config.xml
index 8f75eb9..d945f08 100644
--- a/packages/firefox-config.xml
+++ b/packages/firefox-config.xml
@@ -2,23 +2,30 @@
 <packages>
     <package id="firefox-config" 
              name="Configuration Firefox"
-             revision="3" 
+             revision="%PKG_VERSION%" 
              priority="10" 
              reboot="false">
 
         <depends package-id="firefox" />
 
+        <variable name='PKG_VERSION' value='4' />
         <variable architecture='x86' name='PROG' value='%PROGRAMFILES%\Mozilla Firefox' />
         <variable architecture='x64' name='PROG' value='%PROGRAMFILES(x86)%\Mozilla Firefox' />
+        <variable architecture='x86' name='REG_PATH' value='HKLM\Software\Mozilla\Firefox' />
+        <variable architecture='x64' name='REG_PATH' value='HKLM\Software\Wow6432Node\Mozilla\Firefox' />
+
+        <check type="registry" condition="equals" path="%REG_PATH%\ConfigRevision" value="%PKG_VERSION%" />
 
         <install cmd='%COMSPEC% /C copy /Y "%SOFTWARE%\firefox\autoconf.js" "%PROG%\defaults\pref\"' />
         <install cmd='%COMSPEC% /C copy /Y "%SOFTWARE%\firefox\override.ini" "%PROG%\"' />
         <install cmd='%COMSPEC% /C copy /Y "%SETTINGS%\firefox\firefox.cfg" "%PROG%\"' />
+        <install cmd='%COMSPEC% /C reg add "%REG_PATH%" /v "ConfigRevision" /t REG_SZ /d "%PKG_VERSION%" /f' />
 
         <upgrade include="install" />
 
         <remove cmd='%COMSPEC% /C del /F "%PROG%\defaults\pref\autoconf.js"' />
         <remove cmd='%COMSPEC% /C del /F "%PROG%\override.ini"' />
         <remove cmd='%COMSPEC% /C del /F "%PROG%\firefox.cfg"' />
+        <remove cmd='%COMSPEC% /C reg delete "%REG_PATH%" /v "ConfigRevision" /f' />
     </package>
 </packages>