--- a/editor/libeditor/HTMLEditor.cpp
+++ b/editor/libeditor/HTMLEditor.cpp
@@ -1768,17 +1768,17 @@ HTMLEditor::GetCSSBackgroundColorState(b
         }
       }
       nodeToExamine = nodeToExamine->GetParentNode();
     } while ( aOutColor.EqualsLiteral("transparent") && nodeToExamine );
   }
   return NS_OK;
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::GetHTMLBackgroundColorState(bool* aMixed,
                                         nsAString& aOutColor)
 {
   //TODO: We don't handle "mixed" correctly!
   NS_ENSURE_TRUE(aMixed, NS_ERROR_NULL_POINTER);
   *aMixed = false;
   aOutColor.Truncate();
 

--- a/editor/libeditor/HTMLEditor.h
+++ b/editor/libeditor/HTMLEditor.h
@@ -152,17 +152,17 @@ public:
   nsresult CopyLastEditableChildStyles(nsINode* aPreviousBlock,
                                        nsINode* aNewBlock,
                                        Element** aOutBrNode);
 
   nsresult LoadHTML(const nsAString& aInputString);
 
   nsresult GetCSSBackgroundColorState(bool* aMixed, nsAString& aOutColor,
                                       bool aBlockLevel);
-  NS_IMETHOD GetHTMLBackgroundColorState(bool* aMixed, nsAString& outColor);
+  nsresult GetHTMLBackgroundColorState(bool* aMixed, nsAString& outColor);
 
   // nsIEditorStyleSheets methods
   NS_DECL_NSIEDITORSTYLESHEETS
 
   // nsIEditorMailSupport methods
   NS_DECL_NSIEDITORMAILSUPPORT
 
   // nsITableEditor methods
@@ -533,37 +533,37 @@ protected:
   // Table Editing (implemented in nsTableEditor.cpp)
 
   /**
    * Insert a new cell after or before supplied aCell.
    * Optional: If aNewCell supplied, returns the newly-created cell (addref'd,
    * of course)
    * This doesn't change or use the current selection.
    */
-  NS_IMETHOD InsertCell(nsIDOMElement* aCell, int32_t aRowSpan,
-                        int32_t aColSpan, bool aAfter, bool aIsHeader,
-                        nsIDOMElement** aNewCell);
+  nsresult InsertCell(nsIDOMElement* aCell, int32_t aRowSpan,
+                      int32_t aColSpan, bool aAfter, bool aIsHeader,
+                      nsIDOMElement** aNewCell);
 
   /**
    * Helpers that don't touch the selection or do batch transactions.
    */
-  NS_IMETHOD DeleteRow(nsIDOMElement* aTable, int32_t aRowIndex);
-  NS_IMETHOD DeleteColumn(nsIDOMElement* aTable, int32_t aColIndex);
-  NS_IMETHOD DeleteCellContents(nsIDOMElement* aCell);
+  nsresult DeleteRow(nsIDOMElement* aTable, int32_t aRowIndex);
+  nsresult DeleteColumn(nsIDOMElement* aTable, int32_t aColIndex);
+  nsresult DeleteCellContents(nsIDOMElement* aCell);
 
   /**
    * Move all contents from aCellToMerge into aTargetCell (append at end).
    */
-  NS_IMETHOD MergeCells(nsCOMPtr<nsIDOMElement> aTargetCell,
-                        nsCOMPtr<nsIDOMElement> aCellToMerge,
-                        bool aDeleteCellToMerge);
+  nsresult MergeCells(nsCOMPtr<nsIDOMElement> aTargetCell,
+                      nsCOMPtr<nsIDOMElement> aCellToMerge,
+                      bool aDeleteCellToMerge);
 
   nsresult DeleteTable2(nsIDOMElement* aTable, Selection* aSelection);
-  NS_IMETHOD SetColSpan(nsIDOMElement* aCell, int32_t aColSpan);
-  NS_IMETHOD SetRowSpan(nsIDOMElement* aCell, int32_t aRowSpan);
+  nsresult SetColSpan(nsIDOMElement* aCell, int32_t aColSpan);
+  nsresult SetRowSpan(nsIDOMElement* aCell, int32_t aRowSpan);
 
   /**
    * Helper used to get nsTableWrapperFrame for a table.
    */
   nsTableWrapperFrame* GetTableFrame(nsIDOMElement* aTable);
 
   /**
    * Needed to do appropriate deleting when last cell or row is about to be
@@ -591,39 +591,39 @@ protected:
    * Returns NS_EDITOR_ELEMENT_NOT_FOUND if cell is not found even if aCell is
    * null.
    */
   nsresult GetCellContext(Selection** aSelection, nsIDOMElement** aTable,
                           nsIDOMElement** aCell, nsIDOMNode** aCellParent,
                           int32_t* aCellOffset, int32_t* aRowIndex,
                           int32_t* aColIndex);
 
-  NS_IMETHOD GetCellSpansAt(nsIDOMElement* aTable, int32_t aRowIndex,
-                            int32_t aColIndex, int32_t& aActualRowSpan,
-                            int32_t& aActualColSpan);
+  nsresult GetCellSpansAt(nsIDOMElement* aTable, int32_t aRowIndex,
+                          int32_t aColIndex, int32_t& aActualRowSpan,
+                          int32_t& aActualColSpan);
 
-  NS_IMETHOD SplitCellIntoColumns(nsIDOMElement* aTable, int32_t aRowIndex,
-                                  int32_t aColIndex, int32_t aColSpanLeft,
-                                  int32_t aColSpanRight,
-                                  nsIDOMElement** aNewCell);
+  nsresult SplitCellIntoColumns(nsIDOMElement* aTable, int32_t aRowIndex,
+                                int32_t aColIndex, int32_t aColSpanLeft,
+                                int32_t aColSpanRight,
+                                nsIDOMElement** aNewCell);
 
-  NS_IMETHOD SplitCellIntoRows(nsIDOMElement* aTable, int32_t aRowIndex,
-                               int32_t aColIndex, int32_t aRowSpanAbove,
-                               int32_t aRowSpanBelow, nsIDOMElement** aNewCell);
+  nsresult SplitCellIntoRows(nsIDOMElement* aTable, int32_t aRowIndex,
+                             int32_t aColIndex, int32_t aRowSpanAbove,
+                             int32_t aRowSpanBelow, nsIDOMElement** aNewCell);
 
   nsresult CopyCellBackgroundColor(nsIDOMElement* destCell,
                                    nsIDOMElement* sourceCell);
 
   /**
    * Reduce rowspan/colspan when cells span into nonexistent rows/columns.
    */
-  NS_IMETHOD FixBadRowSpan(nsIDOMElement* aTable, int32_t aRowIndex,
-                           int32_t& aNewRowCount);
-  NS_IMETHOD FixBadColSpan(nsIDOMElement* aTable, int32_t aColIndex,
-                           int32_t& aNewColCount);
+  nsresult FixBadRowSpan(nsIDOMElement* aTable, int32_t aRowIndex,
+                         int32_t& aNewRowCount);
+  nsresult FixBadColSpan(nsIDOMElement* aTable, int32_t aColIndex,
+                         int32_t& aNewColCount);
 
   /**
    * Fallback method: Call this after using ClearSelection() and you
    * failed to set selection to some other content in the document.
    */
   nsresult SetSelectionAtDocumentStart(Selection* aSelection);
 
   nsresult GetTableSize(Element* aTable,
@@ -655,30 +655,30 @@ protected:
    */
   bool IsTextPropertySetByContent(nsINode* aNode,
                                   nsAtom* aProperty,
                                   nsAtom* aAttribute,
                                   const nsAString* aValue,
                                   nsAString* outValue = nullptr);
 
   // Methods for handling plaintext quotations
-  NS_IMETHOD PasteAsPlaintextQuotation(int32_t aSelectionType);
+  nsresult PasteAsPlaintextQuotation(int32_t aSelectionType);
 
   /**
    * Insert a string as quoted text, replacing the selected text (if any).
    * @param aQuotedText     The string to insert.
    * @param aAddCites       Whether to prepend extra ">" to each line
    *                        (usually true, unless those characters
    *                        have already been added.)
    * @return aNodeInserted  The node spanning the insertion, if applicable.
    *                        If aAddCites is false, this will be null.
    */
-  NS_IMETHOD InsertAsPlaintextQuotation(const nsAString& aQuotedText,
-                                        bool aAddCites,
-                                        nsIDOMNode** aNodeInserted);
+  nsresult InsertAsPlaintextQuotation(const nsAString& aQuotedText,
+                                      bool aAddCites,
+                                      nsIDOMNode** aNodeInserted);
 
   nsresult InsertObject(const nsACString& aType, nsISupports* aObject,
                         bool aIsSafe,
                         nsIDOMDocument* aSourceDoc,
                         nsIDOMNode* aDestinationNode,
                         int32_t aDestOffset,
                         bool aDoDeleteSelection);
 

--- a/editor/libeditor/HTMLEditorDataTransfer.cpp
+++ b/editor/libeditor/HTMLEditorDataTransfer.cpp
@@ -1637,17 +1637,17 @@ HTMLEditor::PasteAsCitedQuotation(const 
   NS_ENSURE_SUCCESS(rv, rv);
 
   return Paste(aSelectionType);
 }
 
 /**
  * Paste a plaintext quotation.
  */
-NS_IMETHODIMP
+nsresult
 HTMLEditor::PasteAsPlaintextQuotation(int32_t aSelectionType)
 {
   // Get Clipboard Service
   nsresult rv;
   nsCOMPtr<nsIClipboard> clipboard(do_GetService("@mozilla.org/widget/clipboard;1", &rv));
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Create generic Transferable for getting the data
@@ -1794,17 +1794,17 @@ HTMLEditor::InsertAsQuotation(const nsAS
   return InsertAsCitedQuotation(aQuotedText, citation, false,
                                 aNodeInserted);
 }
 
 // Insert plaintext as a quotation, with cite marks (e.g. "> ").
 // This differs from its corresponding method in TextEditor
 // in that here, quoted material is enclosed in a <pre> tag
 // in order to preserve the original line wrapping.
-NS_IMETHODIMP
+nsresult
 HTMLEditor::InsertAsPlaintextQuotation(const nsAString& aQuotedText,
                                        bool aAddCites,
                                        nsIDOMNode** aNodeInserted)
 {
   // get selection
   RefPtr<Selection> selection = GetSelection();
   NS_ENSURE_TRUE(selection, NS_ERROR_NULL_POINTER);
 

--- a/editor/libeditor/HTMLTableEditor.cpp
+++ b/editor/libeditor/HTMLTableEditor.cpp
@@ -82,17 +82,17 @@ public:
   //  when one method yields control to another
   void CancelSetCaret()
   {
     mHTMLEditor = nullptr;
     mTable = nullptr;
   }
 };
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::InsertCell(nsIDOMElement* aDOMCell,
                        int32_t aRowSpan,
                        int32_t aColSpan,
                        bool aAfter,
                        bool aIsHeader,
                        nsIDOMElement** aNewDOMCell)
 {
   if (aNewDOMCell) {
@@ -149,27 +149,27 @@ HTMLEditor::InsertCell(nsIDOMElement* aD
       "Failed to advance offset to after the old cell");
   }
 
   // Don't let Rules System change the selection.
   AutoTransactionsConserveSelection dontChangeSelection(this);
   return InsertNode(*newCell, pointToInsert.AsRaw());
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::SetColSpan(nsIDOMElement* aCell,
                        int32_t aColSpan)
 {
   NS_ENSURE_TRUE(aCell, NS_ERROR_NULL_POINTER);
   nsAutoString newSpan;
   newSpan.AppendInt(aColSpan, 10);
   return SetAttribute(aCell, NS_LITERAL_STRING("colspan"), newSpan);
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::SetRowSpan(nsIDOMElement* aCell,
                        int32_t aRowSpan)
 {
   NS_ENSURE_TRUE(aCell, NS_ERROR_NULL_POINTER);
   nsAutoString newSpan;
   newSpan.AppendInt(aRowSpan, 10);
   return SetAttribute(aCell, NS_LITERAL_STRING("rowspan"), newSpan);
 }
@@ -982,17 +982,17 @@ HTMLEditor::DeleteTableCellContents()
       NS_ENSURE_SUCCESS(rv, rv);
     } else {
       cell = nullptr;
     }
   }
   return NS_OK;
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::DeleteCellContents(nsIDOMElement* aCell)
 {
   NS_ENSURE_TRUE(aCell, NS_ERROR_NULL_POINTER);
 
   // Prevent rules testing until we're done
   AutoRules beginRulesSniffing(this, EditAction::deleteNode, nsIEditor::eNext);
 
   nsCOMPtr<nsIDOMNode> child;
@@ -1084,17 +1084,17 @@ HTMLEditor::DeleteTableColumn(int32_t aN
     for (int32_t i = 0; i < aNumber; i++) {
       rv = DeleteColumn(table, startColIndex);
       NS_ENSURE_SUCCESS(rv, rv);
     }
   }
   return NS_OK;
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::DeleteColumn(nsIDOMElement* aTable,
                          int32_t aColIndex)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
 
   nsCOMPtr<nsIDOMElement> cell;
   int32_t startRowIndex, startColIndex, rowSpan, colSpan, actualRowSpan, actualColSpan;
   bool    isSelected;
@@ -1261,17 +1261,17 @@ HTMLEditor::DeleteTableRow(int32_t aNumb
         break;
       }
     }
   }
   return NS_OK;
 }
 
 // Helper that doesn't batch or change the selection
-NS_IMETHODIMP
+nsresult
 HTMLEditor::DeleteRow(nsIDOMElement* aTable,
                       int32_t aRowIndex)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
 
   nsCOMPtr<nsIDOMElement> cell;
   nsCOMPtr<nsIDOMElement> cellInDeleteRow;
   int32_t startRowIndex, startColIndex, rowSpan, colSpan, actualRowSpan, actualColSpan;
@@ -1790,17 +1790,17 @@ HTMLEditor::CopyCellBackgroundColor(nsID
     return rv;
   }
   if (!isSet) {
     return NS_OK;
   }
   return SetAttribute(destCell, bgcolor, color);
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::SplitCellIntoColumns(nsIDOMElement* aTable,
                                  int32_t aRowIndex,
                                  int32_t aColIndex,
                                  int32_t aColSpanLeft,
                                  int32_t aColSpanRight,
                                  nsIDOMElement** aNewCell)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
@@ -1838,17 +1838,17 @@ HTMLEditor::SplitCellIntoColumns(nsIDOME
     return NS_OK;
   }
   if (aNewCell) {
     NS_ADDREF(*aNewCell = newCell.get());
   }
   return CopyCellBackgroundColor(newCell, cell);
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::SplitCellIntoRows(nsIDOMElement* aTable,
                               int32_t aRowIndex,
                               int32_t aColIndex,
                               int32_t aRowSpanAbove,
                               int32_t aRowSpanBelow,
                               nsIDOMElement** aNewCell)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
@@ -2303,17 +2303,17 @@ HTMLEditor::JoinTableCells(bool aMergeNo
 
     // Reset target cell's colspan to encompass cell to the right
     rv = SetColSpan(targetCell, actualColSpan+actualColSpan2);
     NS_ENSURE_SUCCESS(rv, rv);
   }
   return NS_OK;
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::MergeCells(nsCOMPtr<nsIDOMElement> aTargetCell,
                        nsCOMPtr<nsIDOMElement> aCellToMerge,
                        bool aDeleteCellToMerge)
 {
   nsCOMPtr<dom::Element> targetCell = do_QueryInterface(aTargetCell);
   nsCOMPtr<dom::Element> cellToMerge = do_QueryInterface(aCellToMerge);
   NS_ENSURE_TRUE(targetCell && cellToMerge, NS_ERROR_NULL_POINTER);
 
@@ -2355,17 +2355,17 @@ HTMLEditor::MergeCells(nsCOMPtr<nsIDOMEl
   if (aDeleteCellToMerge) {
     return DeleteNode(aCellToMerge);
   }
 
   return NS_OK;
 }
 
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::FixBadRowSpan(nsIDOMElement* aTable,
                           int32_t aRowIndex,
                           int32_t& aNewRowCount)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
 
   int32_t rowCount, colCount;
   nsresult rv = GetTableSize(aTable, &rowCount, &colCount);
@@ -2420,17 +2420,17 @@ HTMLEditor::FixBadRowSpan(nsIDOMElement*
         }
       }
       NS_ASSERTION((actualColSpan > 0),"ActualColSpan = 0 in FixBadRowSpan");
     }
   }
   return GetTableSize(aTable, &aNewRowCount, &colCount);
 }
 
-NS_IMETHODIMP
+nsresult
 HTMLEditor::FixBadColSpan(nsIDOMElement* aTable,
                           int32_t aColIndex,
                           int32_t& aNewColCount)
 {
   NS_ENSURE_TRUE(aTable, NS_ERROR_NULL_POINTER);
 
   int32_t rowCount, colCount;
   nsresult rv = GetTableSize(aTable, &rowCount, &colCount);
@@ -2780,17 +2780,17 @@ HTMLEditor::GetCellAt(nsIDOMElement* aTa
   nsCOMPtr<nsIDOMElement> domCell =
     do_QueryInterface(tableFrame->GetCellAt(aRowIndex, aColIndex));
   domCell.forget(aCell);
 
   return NS_OK;
 }
 
 // When all you want are the rowspan and colspan (not exposed in nsITableEditor)
-NS_IMETHODIMP
+nsresult
 HTMLEditor::GetCellSpansAt(nsIDOMElement* aTable,
                            int32_t aRowIndex,
                            int32_t aColIndex,
                            int32_t& aActualRowSpan,
                            int32_t& aActualColSpan)
 {
   nsTableWrapperFrame* tableFrame = GetTableFrame(aTable);
   if (!tableFrame) {