new file mode 100644
--- /dev/null
+++ b/mail/test/mozmill/composition/test-signature-updating.js
@@ -0,0 +1,180 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is mozilla.org code.
+ *
+ * The Initial Developer of the Original Code is
+ * Steffen Wilberg <steffen.wilberg@web.de>
+ * Portions created by the Initial Developer are Copyright (C) 2010
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+/**
+ * Tests that the signature updates properly when switching identities.
+ */
+
+// make SOLO_TEST=composition/test-signature-updating.js mozmill-one
+
+// mail.identity.id1.htmlSigFormat = false
+// mail.identity.id1.htmlSigText   = "Tinderbox is soo 90ies"
+
+// mail.identity.id2.htmlSigFormat = true
+// mail.identity.id2.htmlSigText   = "Tinderboxpushlog is the new <b>hotness!</b>"
+
+const MODULE_NAME = "test-signature-updating";
+
+const RELATIVE_ROOT = "../shared-modules";
+const MODULE_REQUIRES = ["folder-display-helpers", "compose-helpers", "window-helpers"];
+var jumlib = {};
+Components.utils.import("resource://mozmill/modules/jum.js", jumlib);
+var elib = {};
+Components.utils.import("resource://mozmill/modules/elementslib.js", elib);
+
+var composeHelper = null;
+var cwc = null; // compose window controller
+var prefBranch = Cc["@mozilla.org/preferences-service;1"]
+                   .getService(Ci.nsIPrefService).getBranch(null);
+
+var setupModule = function (module) {
+  let fdh = collector.getModule("folder-display-helpers");
+  fdh.installInto(module);
+  composeHelper = collector.getModule("compose-helpers");
+  composeHelper.installInto(module);
+  let wh = collector.getModule("window-helpers");
+  wh.installInto(module);
+};
+
+function setupComposeWin(toAddr, subj, body) {
+  cwc.type(cwc.a("addressingWidget", {class: "addressingWidgetCell", crazyDeck: 1}), toAddr);
+  cwc.type(cwc.eid("msgSubject"), subj)
+  cwc.type(cwc.eid("content-frame"), body);
+}
+
+/**
+ * Test that the plaintext compose window has a signature initially,
+ * and has the correct signature after switching to another identity.
+ */
+function testPlaintextComposeWindowSwitchSignatures() {
+  prefBranch.setBoolPref("mail.identity.id1.compose_html", false);
+  cwc = composeHelper.open_compose_new_mail();
+
+  setupComposeWin("", "Plaintext compose window", "Body, first line.");
+
+  let contentFrame = cwc.e("content-frame");
+  let node = contentFrame.contentDocument.body.lastChild;
+
+  // In plaintext compose, the signature is followed by two <br> elements.
+  assert_equals(node.localName, "br");
+  node = node.previousSibling;
+  assert_equals(node.localName, "br");
+  node = node.previousSibling;
+  assert_equals(node.nodeValue, "Tinderbox is soo 90ies");
+  node = node.previousSibling.previousSibling; // a <br> element, then the next text node
+  assert_equals(node.nodeValue, "-- ");
+
+  // Now switch identities!
+  let menuID = cwc.e("msgIdentity");
+  menuID.value = "id2";
+  menuID.click();
+
+  node = contentFrame.contentDocument.body.lastChild;
+
+  // In plaintext compose, the signature is followed by two <br> elements.
+  assert_equals(node.localName, "br");
+  node = node.previousSibling;
+  assert_equals(node.localName, "br");
+  node = node.previousSibling;
+  assert_equals(node.nodeValue, "Tinderboxpushlog is the new *hotness!*");
+  node = node.previousSibling.previousSibling; // a <br> element, then the next text node
+  assert_equals(node.nodeValue, "-- ");
+
+  // Now check that the original signature has been removed!
+  let bodyFirstChild =  contentFrame.contentDocument.body.firstChild;
+  while (node != bodyFirstChild) {
+    node = node.previousSibling;
+    jumlib.assertNotEquals(node.nodeValue, "Tinderbox is soo 90ies");
+    jumlib.assertNotEquals(node.nodeValue, "-- ");
+  }
+  assert_equals(node.nodeValue, "Body, first line.");
+
+  composeHelper.close_compose_window(cwc);
+}
+
+/**
+ * Same test, but with an HTML compose window
+ */
+function testHTMLComposeWindowSwitchSignatures() {
+  prefBranch.setBoolPref("mail.identity.id1.compose_html", true);
+  cwc = composeHelper.open_compose_new_mail();
+
+  setupComposeWin("", "HTML compose window", "Body, first line.");
+
+  let contentFrame = cwc.e("content-frame");
+  let node = contentFrame.contentDocument.body.lastChild;
+
+  // In html compose, the signature is inside the last node, which has a
+  // class="moz-signature".
+  assert_equals(node.className, "moz-signature")
+  node = node.firstChild; // text node containing the signature divider
+  assert_equals(node.nodeValue, "-- \nTinderbox is soo 90ies");
+
+  // Now switch identities!
+  let menuID = cwc.e("msgIdentity");
+  menuID.value = "id2";
+  menuID.click();
+
+  node = contentFrame.contentDocument.body.lastChild;
+
+  // In html compose, the signature is inside the last node
+  // with class="moz-signature".
+  assert_equals(node.className, "moz-signature");
+  node = node.firstChild; // text node containing the signature divider
+  assert_equals(node.nodeValue, "-- ");
+  node = node.nextSibling;
+  assert_equals(node.localName, "br");
+  node = node.nextSibling;
+  assert_equals(node.nodeValue, "Tinderboxpushlog is the new ");
+  node = node.nextSibling;
+  assert_equals(node.localName, "b");
+  node = node.firstChild;
+  assert_equals(node.nodeValue, "hotness!");
+
+  // Now check that the original signature has been removed,
+  // and no blank lines got added!
+  node = contentFrame.contentDocument.body.firstChild;
+  assert_equals(node.nodeValue, "Body, first line.");
+  node = node.nextSibling;
+  assert_equals(node.localName, "br");
+  node = node.nextSibling;
+  // check that the signature is immediately after the message text.
+  assert_equals(node.className, "moz-signature");
+  // check that that the signature is the last node.
+  assert_equals(node, contentFrame.contentDocument.body.lastChild);
+
+  composeHelper.close_compose_window(cwc);
+}

--- a/mail/test/mozmill/mozmilltests.list
+++ b/mail/test/mozmill/mozmilltests.list
@@ -1,17 +1,18 @@
-folder-display
-junk-commands
-search-window
-cookies
+account
+composition/test-signature-updating.js
 content-policy
 content-tabs
-message-header
+cookies
+folder-display
+folder-pane
+folder-tree-modes
 folder-widget
-folder-pane
+junk-commands
+message-header
 message-window
-session-store
-pref-window
-folder-tree-modes
-quick-filter-bar
 migration
 migration-from-tb2
-account
+pref-window
+quick-filter-bar
+search-window
+session-store

--- a/mail/test/mozmill/runtest.py
+++ b/mail/test/mozmill/runtest.py
@@ -117,25 +117,33 @@ class ThunderTestProfile(mozrunner.Thund
         # disable address books for undisclosed reasons
         'ldap_2.servers.osx.position': 0,
         'ldap_2.servers.oe.position': 0,
         # disable the first use junk dialog
         'mailnews.ui.junk.firstuse': False,
         # other unknown voodoo
         # -- dummied up local accounts to stop the account wizard
         'mail.account.account1.server' :  "server1",
-        'mail.account.account2.identities' :  "id1",
+        'mail.account.account2.identities' :  "id1,id2",
         'mail.account.account2.server' :  "server2",
         'mail.accountmanager.accounts' :  "account1,account2",
         'mail.accountmanager.defaultaccount' :  "account2",
         'mail.accountmanager.localfoldersserver' :  "server1",
         'mail.identity.id1.fullName' :  "Tinderbox",
+        'mail.identity.id1.htmlSigFormat' : False,
+        'mail.identity.id1.htmlSigText' : "Tinderbox is soo 90ies",
         'mail.identity.id1.smtpServer' :  "smtp1",
         'mail.identity.id1.useremail' :  "tinderbox@invalid.com",
         'mail.identity.id1.valid' :  True,
+        'mail.identity.id2.fullName' : "Tinderboxpushlog",
+        'mail.identity.id2.htmlSigFormat' : True,
+        'mail.identity.id2.htmlSigText' : "Tinderboxpushlog is the new <b>hotness!</b>",
+        'mail.identity.id2.smtpServer' : "smtp1",
+        'mail.identity.id2.useremail' : "tinderboxpushlog@invalid.com",
+        'mail.identity.id2.valid' : True,
         'mail.root.none-rel' :  "[ProfD]Mail",
         'mail.root.pop3-rel' :  "[ProfD]Mail",
         'mail.server.server1.directory-rel' :  "[ProfD]Mail/Local Folders",
         'mail.server.server1.hostname' :  "Local Folders",
         'mail.server.server1.name' :  "Local Folders",
         'mail.server.server1.type' :  "none",
         'mail.server.server1.userName' :  "nobody",
         'mail.server.server2.check_new_mail' :  False,

--- a/mailnews/compose/src/nsMsgCompose.cpp
+++ b/mailnews/compose/src/nsMsgCompose.cpp
@@ -4124,17 +4124,17 @@ nsMsgCompose::ProcessSignature(nsIMsgIde
   if (identity && !attachFile)
     identity->GetHtmlSigText(prefSigText);
   // Now, if they didn't even want to use a signature, we should
   // just return nicely.
   //
   if ((!useSigFile  && prefSigText.IsEmpty()) || NS_FAILED(rv))
     return NS_OK;
 
-  static const char      htmlBreak[] = "<BR>";
+  static const char      htmlBreak[] = "<br>";
   static const char      dashes[] = "-- ";
   static const char      htmlsigopen[] = "<div class=\"moz-signature\">";
   static const char      htmlsigclose[] = "</div>";    /* XXX: Due to a bug in
                              4.x' HTML editor, it will not be able to
                              break this HTML sig, if quoted (for the user to
                              interleave a comment). */
   static const char      _preopen[] = "<pre class=\"moz-signature\" cols=%d>";
   char*                  preopen;
@@ -5326,17 +5326,17 @@ nsMsgCompose::SetIdentity(nsIMsgIdentity
               m_editor->EndTransaction();
               return rv;
             }
 
             //Also, remove the <br> right before the signature.
             if (tempNode)
             {
               tempNode->GetLocalName(tagLocalName);
-              if (tagLocalName.EqualsLiteral("BR"))
+              if (tagLocalName.EqualsLiteral("br"))
                 m_editor->DeleteNode(tempNode);
             }
             m_editor->EndTransaction();
           }
         }
       }
     }
     else
@@ -5347,39 +5347,39 @@ nsMsgCompose::SetIdentity(nsIMsgIdentity
 
       do
       {
         node->GetNodeType(&nodeType);
         node->GetLocalName(tagLocalName);
         switch (searchState)
         {
           case 0:
-            if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("BR"))
+            if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("br"))
               searchState = 1;
             break;
 
           case 1:
             searchState = 0;
             if (nodeType == nsIDOMNode::TEXT_NODE)
             {
               nsString nodeValue;
               node->GetNodeValue(nodeValue);
               if (nodeValue.EqualsLiteral("-- "))
                 searchState = 2;
             }
             else
-              if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("BR"))
+              if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("br"))
               {
                 searchState = 1;
                 break;
               }
             break;
 
           case 2:
-            if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("BR"))
+            if (nodeType == nsIDOMNode::ELEMENT_NODE && tagLocalName.EqualsLiteral("br"))
               searchState = 3;
             else
               searchState = 0;
             break;
         }
 
         tempNode = node;
       } while (searchState != 3 && NS_SUCCEEDED(tempNode->GetPreviousSibling(getter_AddRefs(node))) && node);