diff --git a/mozilla/editor/libeditor/html/nsHTMLCSSUtils.cpp b/mozilla/editor/libeditor/html/nsHTMLCSSUtils.cpp
index 0e086971dfc..6cee18abeed 100644
--- a/mozilla/editor/libeditor/html/nsHTMLCSSUtils.cpp
+++ b/mozilla/editor/libeditor/html/nsHTMLCSSUtils.cpp
@@ -74,6 +74,24 @@ void ProcessBValue(nsAReadableString * aInputString, nsAWritableString & aOutput
   }
 }
 
+static
+void ProcessIValue(nsAReadableString * aInputString, nsAWritableString & aOutputString,
+                   const char * aDefaultValueString,
+                   const char * aPrependString, const char* aAppendString)
+{
+  if (aInputString) {
+    if (aInputString->Equals(NS_LITERAL_STRING("-moz-editor-invert-value"))) {
+      aOutputString.Assign(NS_LITERAL_STRING("normal"));
+    }
+    else {
+      aOutputString.Assign(NS_LITERAL_STRING("italic"));
+    }
+  }
+  else {
+    aOutputString.Assign(NS_LITERAL_STRING("italic"));
+  }
+}
+
 static
 void ProcessDefaultValue(nsAReadableString * aInputString, nsAWritableString & aOutputString,
                          const char * aDefaultValueString,
@@ -205,7 +223,7 @@ const nsHTMLCSSUtils::CSSEquivTable boldEquivTable[] = {
 };
 
 const nsHTMLCSSUtils::CSSEquivTable italicEquivTable[] = {
-  { nsHTMLCSSUtils::eCSSEditableProperty_font_style, ProcessDefaultValue, "italic", nsnull, nsnull, PR_TRUE },
+  { nsHTMLCSSUtils::eCSSEditableProperty_font_style, ProcessIValue, nsnull, nsnull, nsnull, PR_TRUE },
   { nsHTMLCSSUtils::eCSSEditableProperty_NONE, 0 }
 };
 
@@ -643,7 +661,8 @@ nsHTMLCSSUtils::RemoveCSSInlineStyle(nsIDOMNode *aNode, nsIAtom *aProperty, nsAR
 PRBool
 nsHTMLCSSUtils::IsCSSInvertable(nsIAtom *aProperty, const nsAReadableString *aAttribute)
 {
-  return PRBool(nsIEditProperty::b == aProperty);
+  return PRBool(nsIEditProperty::b == aProperty
+                || nsIEditProperty::i == aProperty);
 }
 
 // Get the default browser background color if we need it for GetCSSBackgroundColorState
diff --git a/mozilla/editor/libeditor/html/nsHTMLEditor.h b/mozilla/editor/libeditor/html/nsHTMLEditor.h
index 70f35957b95..82d5a847632 100644
--- a/mozilla/editor/libeditor/html/nsHTMLEditor.h
+++ b/mozilla/editor/libeditor/html/nsHTMLEditor.h
@@ -719,6 +719,8 @@ protected:
                              PRBool *aAll,
                              nsAWritableString *outValue);
 
+  nsresult RemoveElementIfUselessSpan(nsIDOMElement * aElement);
+
 // Data members
 protected:
 
diff --git a/mozilla/editor/libeditor/html/nsHTMLEditorStyle.cpp b/mozilla/editor/libeditor/html/nsHTMLEditorStyle.cpp
index bd0d0919e03..d7a7545886f 100644
--- a/mozilla/editor/libeditor/html/nsHTMLEditorStyle.cpp
+++ b/mozilla/editor/libeditor/html/nsHTMLEditorStyle.cpp
@@ -334,7 +334,11 @@ nsHTMLEditor::SetInlinePropertyOnTextNode( nsIDOMCharacterData *aTextNode,
   PRBool bHasProp;
   nsCOMPtr<nsIDOMNode> styleNode;
   IsTextPropertySetByContent(node, aProperty, aAttribute, aValue, bHasProp, getter_AddRefs(styleNode));
-  if (bHasProp) return NS_OK;
+  if (bHasProp &&
+      !(aValue && aValue->Equals(NS_LITERAL_STRING("-moz-editor-invert-value"))))
+  {
+    return NS_OK;
+  }
   
   // do we need to split the text node?
   PRUint32 textLen;
@@ -420,10 +424,32 @@ nsHTMLEditor::SetInlinePropertyOnNode( nsIDOMNode *aNode,
       // children of the aNode
       res = RemoveStyleInside(tmp, aProperty, aAttribute, PR_TRUE);
       if (NS_FAILED(res)) return res;
-      PRInt32 count;
-      // then we add the css styles corresponding to the HTML style request
-      res = mHTMLCSSUtils->SetCSSEquivalentToHTMLStyle(element, aProperty, aAttribute, aValue, &count);
+      nsCOMPtr<nsIDOMNode> parentNode;
+      res = tmp->GetParentNode(getter_AddRefs(parentNode));
       if (NS_FAILED(res)) return res;
+      PRBool isSet = PR_FALSE;
+      if (parentNode) {
+        // let's check if the parent element already has the style we want
+        nsAutoString parentValue;
+        mHTMLCSSUtils->IsCSSEquivalentToHTMLInlineStyleSet(parentNode, aProperty, aAttribute,
+                                                           isSet, parentValue,
+                                                           COMPUTED_STYLE_TYPE);
+      }
+      if (isSet && !(aValue && aValue->Equals(NS_LITERAL_STRING("-moz-editor-invert-value")))) {
+        // the parent has the style we want to apply and we are not trying to remove this style
+        // from the selection
+        res = mHTMLCSSUtils->RemoveCSSEquivalentToHTMLStyle(element,
+                                                      aProperty,
+                                                      aAttribute,
+                                                      aValue);
+        if (NS_FAILED(res)) return res;
+        res = RemoveElementIfUselessSpan(element);
+      }
+      else {
+        PRInt32 count;
+        // add the css styles corresponding to the HTML style request
+        res = mHTMLCSSUtils->SetCSSEquivalentToHTMLStyle(element, aProperty, aAttribute, aValue, &count);
+      }
       return res;
     }
   }
@@ -695,21 +721,9 @@ nsresult nsHTMLEditor::RemoveStyleInside(nsIDOMNode *aNode,
                                                       aProperty,
                                                       aAttribute,
                                                       &propertyValue);
-        // remove the node if it is a span, if its style attribute is empty or absent,
-        // and if it does not have a class nor an id
-        nsCOMPtr<nsIDOMElement> elem = do_QueryInterface(aNode);
-        nsAutoString styleVal;
-        PRBool isStyleSet;
-        res = GetAttributeValue(elem,  NS_LITERAL_STRING("style"), styleVal, &isStyleSet);
+        nsCOMPtr<nsIDOMElement> element = do_QueryInterface(aNode);
+        res = RemoveElementIfUselessSpan(element);
         if (NS_FAILED(res)) return res;
-        if (NodeIsType(aNode, nsIEditProperty::span) && (!isStyleSet || (0 == styleVal.Length()))) {
-          PRBool hasClassOrId ;
-          res = mHTMLCSSUtils->HasClassOrID(elem, hasClassOrId);
-          if (!hasClassOrId) {
-            res = RemoveContainer(aNode);
-            if (NS_FAILED(res)) return res;
-          }
-        }
       }
     }
   }  
@@ -1822,3 +1836,30 @@ nsHTMLEditor::IsCSSEnabled(PRBool *aIsSet)
   return NS_OK;
 }
 
+nsresult
+nsHTMLEditor::RemoveElementIfUselessSpan(nsIDOMElement * aElement)
+{
+  NS_ENSURE_TRUE(aElement, NS_ERROR_NULL_POINTER);
+  nsCOMPtr<nsIDOMNode> node  = do_QueryInterface(aElement);
+
+  // early way out if node is not a span element
+  if (!NodeIsType(node, nsIEditProperty::span)) {
+    return NS_OK;
+  }
+
+  // remove the node if it is a span, if its style attribute is empty or absent,
+  // and if it does not have a class nor an id
+  nsAutoString styleVal;
+  PRBool isStyleSet;
+  nsresult res = GetAttributeValue(aElement,  NS_LITERAL_STRING("style"), styleVal, &isStyleSet);
+  if (NS_FAILED(res)) return res;
+  if (!isStyleSet || (0 == styleVal.Length())) {
+    PRBool hasClassOrId ;
+    res = mHTMLCSSUtils->HasClassOrID(aElement, hasClassOrId);
+    if (NS_FAILED(res)) return res;
+    if (!hasClassOrId) {
+      res = RemoveContainer(node);
+    }
+  }
+  return res;
+}