Try
               Dim myProfileDirectory() As DirectoryInfo = New DirectoryInfo(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) & "\Mozilla\Firefox\Profiles\").GetDirectories("*.default")
               Dim myFFPrefFile As String = myProfileDirectory(0).FullName & "\prefs.js"
               If File.Exists(myFFPrefFile) Then
                   ' We have a pref file so let's make sure it has the proxy setting
                   Dim myReader As New StreamReader(myFFPrefFile)
                   Dim myPrefContents As String = myReader.ReadToEnd
                   myReader.Close()
                   ' Look for the proxy line
                   Dim myProxyLineIndex As Integer = myPrefContents.IndexOf("user_pref(""network.proxy.type""")
                   If myProxyLineIndex > 0 Then
                       ' We found a proxy line so delete it and add our new one to enable.  This assumes the proxy server/port are already 
                       ' programmed in although you can use the same logic to change those lines
                       myPrefContents = myPrefContents.Remove(myProxyLineIndex, 38)
                       myPrefContents = myPrefContents.Insert(myProxyLineIndex, "user_pref(""network.proxy.type"", 1);")
                       File.Delete(myFFPrefFile)
                       File.WriteAllText(myFFPrefFile, myPrefContents)
                   End If
               End If
           Catch ex As Exception
               ' Only exception should be a read/write error because the user opened up FireFox so they can be ignored.
           End Try

           Try
               Dim myProfileDirectory() As DirectoryInfo = New DirectoryInfo(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) & "\Mozilla\Firefox\Profiles\").GetDirectories("*.default")
               Dim myFFPrefFile As String = myProfileDirectory(0).FullName & "\prefs.js"
               If File.Exists(myFFPrefFile) Then
                   ' We have a pref file so lets make sure it has the proxy setting

                   Dim myReader As New StreamReader(myFFPrefFile)
                   Dim myPrefContents As String = myReader.ReadToEnd
                   myReader.Close()
                   ' Look for the proxy line
                   Dim myProxyLineIndex As Integer = myPrefContents.IndexOf("user_pref(""network.proxy.type""")
                   If myProxyLineIndex > 0 Then
                       ' We found a proxy line so delete it and add our new one to disable it.
                       myPrefContents = myPrefContents.Remove(myProxyLineIndex, 38)
                       myPrefContents = myPrefContents.Insert(myProxyLineIndex, "user_pref(""network.proxy.type"", 0);")
                       File.Delete(myFFPrefFile)
                       File.WriteAllText(myFFPrefFile, myPrefContents)
                   End If
               End If
           Catch ex As Exception
               ' Only exception should be a read/write error because the user opened up FireFox so they can be ignored.
           End Try
       End If

== Issue == I have another kind of problem with Firefox == Description == This is in reference to http://support.mozilla.com/en-US/forum/1/578868 which has been marked answered and closed. There was a change made somewhere between 3.5 and 3.6 that broke the code I wrote, when the proxy line was not in the prefs.js file it assumed no proxy. Now it has to have the proxy line with a 0 to be disabled (missing the line defaults to use system proxy now). So here is a update of my code that I posted in the other thread. Mods - please feel free to copy the contents of this post into the one linked above and delete this one. <code>Enable FireFox Proxy: Try Dim myProfileDirectory() As DirectoryInfo = New DirectoryInfo(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) & "\Mozilla\Firefox\Profiles\").GetDirectories("*.default") Dim myFFPrefFile As String = myProfileDirectory(0).FullName & "\prefs.js" If File.Exists(myFFPrefFile) Then ' We have a pref file so let's make sure it has the proxy setting Dim myReader As New StreamReader(myFFPrefFile) Dim myPrefContents As String = myReader.ReadToEnd myReader.Close() ' Look for the proxy line Dim myProxyLineIndex As Integer = myPrefContents.IndexOf("user_pref(""network.proxy.type""") If myProxyLineIndex > 0 Then ' We found a proxy line so delete it and add our new one to enable. This assumes the proxy server/port are already ' programmed in although you can use the same logic to change those lines myPrefContents = myPrefContents.Remove(myProxyLineIndex, 38) myPrefContents = myPrefContents.Insert(myProxyLineIndex, "user_pref(""network.proxy.type"", 1);") File.Delete(myFFPrefFile) File.WriteAllText(myFFPrefFile, myPrefContents) End If End If Catch ex As Exception ' Only exception should be a read/write error because the user opened up FireFox so they can be ignored. End Try Disable FireFox Proxy: Try Dim myProfileDirectory() As DirectoryInfo = New DirectoryInfo(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) & "\Mozilla\Firefox\Profiles\").GetDirectories("*.default") Dim myFFPrefFile As String = myProfileDirectory(0).FullName & "\prefs.js" If File.Exists(myFFPrefFile) Then ' We have a pref file so let''s make sure it has the proxy setting Dim myReader As New StreamReader(myFFPrefFile) Dim myPrefContents As String = myReader.ReadToEnd myReader.Close() ' Look for the proxy line Dim myProxyLineIndex As Integer = myPrefContents.IndexOf("user_pref(""network.proxy.type""") If myProxyLineIndex > 0 Then ' We found a proxy line so delete it and add our new one to disable it. myPrefContents = myPrefContents.Remove(myProxyLineIndex, 38) myPrefContents = myPrefContents.Insert(myProxyLineIndex, "user_pref(""network.proxy.type"", 0);") File.Delete(myFFPrefFile) File.WriteAllText(myFFPrefFile, myPrefContents) End If End If Catch ex As Exception ' Only exception should be a read/write error because the user opened up FireFox so they can be ignored. End Try End If</code> == This happened == Every time Firefox opened == Firefox version == 3.6.6 == Operating system == Windows XP == User Agent == Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.6) Gecko/20100625 Firefox/3.6.6 ( .NET CLR 3.5.30729) == Plugins installed == *-LogMeIn, Inc. Remote Access Components *Office Plugin for Netscape Navigator *RealPlayer(tm) LiveConnect-Enabled Plug-In *6.0.12.46 *The QuickTime Plugin allows you to view a wide variety of multimedia content in Web pages. For more information, visit the QuickTime Web site. *Default Plug-in *Shockwave Flash 10.1 r53 *4.0.50524.0 *Windows Presentation Foundation (WPF) plug-in for Mozilla browsers *NPRuntime Script Plug-in Library for Java(TM) Deploy *Next Generation Java Plug-in 1.6.0_20 for Mozilla browsers *Adobe PDF Plug-In For Firefox and Netscape *DRM Netscape Network Object *Npdsplay dll *DRM Store Netscape Plugin