Steps to reproduce:
1. Select photos, and do Photos > Export > facebook...

2. Click on the "Login" button.  My browser opens up to the facebook apps page, and I add the App.  However, meanwhile the export has failed with "Error logging into Facebook" and the following on the console (Note, this is non-fatal, if a bit annoying):

FacebookException: Code: 100, Message: Invalid parameter
  at Mono.Facebook.Util.GetResponse[SessionInfo] (System.String method_name, Mono.Facebook.FacebookParam[] parameters) [0x00000] 
  at Mono.Facebook.FacebookSession.GetSessionFromToken (System.String auth_token) [0x00000] 
  at Mono.Facebook.FacebookSession.GetSession () [0x00000] 
  at FSpot.Exporter.Facebook.FacebookAccount.get_Authenticated () [0x00000]

3. From now on when I click the "Login" button of the Facebook export dialog, even after exiting and restarting f-spot, f-spot will crash.

Stack trace:
Marshaling clicked signal
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: There is an error in XML document. ---> System.InvalidOperationException: <friends_get_response xmlns='http://api.facebook.com/1.0/'> was not expected
  at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadRoot (System.Xml.Serialization.XmlTypeMapping rootMap) [0x00000] 
  at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadRoot () [0x00000] 
  at System.Xml.Serialization.XmlSerializer.Deserialize (System.Xml.Serialization.XmlSerializationReader reader) [0x00000] 
  --- End of inner exception stack trace ---
  at System.Xml.Serialization.XmlSerializer.Deserialize (System.Xml.Serialization.XmlSerializationReader reader) [0x00000] 
  at System.Xml.Serialization.XmlSerializer.Deserialize (System.Xml.XmlReader xmlReader) [0x00000] 
  at System.Xml.Serialization.XmlSerializer.Deserialize (System.IO.Stream stream) [0x00000] 
  at Mono.Facebook.Util.GetResponse[FriendsResponse] (System.String method_name, Mono.Facebook.FacebookParam[] parameters) [0x00000] 
  at Mono.Facebook.FacebookSession.GetFriends () [0x00000] 
  at FSpot.Exporter.Facebook.FacebookExport.HandleLoginClicked (System.Object sender, System.EventArgs args) [0x00000] 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  --- End of inner exception stack trace ---
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] 
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] 
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.MarshalCallback (IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data) [0x00000] 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at FSpot.Driver.Main(System.String[] args)

Other information:
Running git commit ID fb1385a21ab593d77c894dc8af1e81bd52ac3504

Browser in question is firefox 3.0.10