diff --git a/layout/mathml/base/src/nsMathMLChar.cpp b/layout/mathml/base/src/nsMathMLChar.cpp
index 61919f28a410..3ab2099de6aa 100644
--- a/layout/mathml/base/src/nsMathMLChar.cpp
+++ b/layout/mathml/base/src/nsMathMLChar.cpp
@@ -51,9 +51,8 @@
 #include "nsCSSRendering.h"
 #include "prprf.h"         // For PR_snprintf()
 
-#include "nsIDOMWindow.h"
-#include "nsIDialogParamBlock.h"
 #include "nsIWindowWatcher.h"
+#include "nsIPrompt.h"
 
 #include "nsMathMLOperators.h"
 #include "nsMathMLChar.h"
@@ -134,46 +133,24 @@ CheckFontExistence(nsIPresContext* aPresContext, const nsString& aFontName)
 }
 
 // alert the user if some of the needed MathML fonts are not installed.
-// it is non-modal (i.e., it doesn't wait for input from the user)
 static void
 AlertMissingFonts(nsString& aMissingFonts)
 {
   nsCOMPtr<nsIWindowWatcher> wwatch(do_GetService("@mozilla.org/embedcomp/window-watcher;1"));
   if (wwatch) {
-    nsCOMPtr<nsIDialogParamBlock> paramBlock(do_CreateInstance("@mozilla.org/embedcomp/dialogparam;1"));
-    if (!paramBlock) return;
-
-    // copied from nsICommonDialogs.idl which curiously isn't part of the build
-    // (mozilla/xpfe/appshell/public/nsICommonDialogs.idl)
-    enum {eMsg=0, eCheckboxMsg=1, eIconClass=2, eTitleMessage=3, eEditfield1Msg=4,
-          eEditfield2Msg=5, eEditfield1Value=6, eEditfield2Value=7, eButton0Text=8,
-          eButton1Text=9, eButton2Text=10, eButton3Text=11,eDialogTitle=12};
-    enum {eButtonPressed=0, eCheckboxState=1, eNumberButtons=2, eNumberEditfields=3,
-          eEditField1Password=4};
-
-    nsAutoString icon;
-    icon.Assign(NS_LITERAL_STRING("alert-icon"));
-
-    nsAutoString title;
-    title.Assign(NS_LITERAL_STRING("Missing MathML Fonts"));
-
-    nsAutoString message;
-    message.Assign(NS_LITERAL_STRING("To properly display the MathML on this page you need to install the following fonts:\n"));
-    message.Append(aMissingFonts);
-    message.Append(NS_LITERAL_STRING(".\n\n\n For further information see:\n http://www.mozilla.org/projects/mathml/fonts"));
-
-    paramBlock->SetInt(eNumberButtons, 1);
-    paramBlock->SetString(eDialogTitle, title.get());
-    paramBlock->SetString(eMsg, message.get());
-    paramBlock->SetString(eIconClass, icon.get());
-
-    nsCOMPtr<nsIDOMWindow> parent;
-    wwatch->GetActiveWindow(getter_AddRefs(parent));
-
-    nsCOMPtr<nsIDOMWindow> dialog;
-    wwatch->OpenWindow(parent, "chrome://global/content/commonDialog.xul", "_blank",
-                       "dependent,centerscreen,chrome,titlebar", paramBlock,
-                       getter_AddRefs(dialog));
+    nsCOMPtr<nsIPrompt> prompter;
+    wwatch->GetNewPrompter(0, getter_AddRefs(prompter));
+    if (prompter) {
+      nsAutoString message;
+      message.AssignWithConversion(
+"This page contains MathML. Mozilla has detected that some "
+"of the fonts needed for quality rendering of MathML are missing "
+"from your system. Without these fonts, Mozilla cannot render "
+"the page properly. To get a rendering of professional quality "
+"you should install the following fonts: ");
+      message.Append(aMissingFonts);
+      prompter->Alert(0, message.get());
+    }
   }
 }
 
@@ -2043,21 +2020,21 @@ nsMathMLChar::PaintVertically(nsIPresContext*      aPresContext,
   // draw top, middle, bottom
   for (i = 0; i < 3; i++) {
     ch = chdata[i];
+#ifdef SHOW_BORDERS
+    // bounding box of the part
+    aRenderingContext.SetColor(NS_RGB(0,0,0));
+    aRenderingContext.DrawRect(nsRect(dx,start[i],width+30*(i+1),end[i]-start[i]));
+#endif
     // glue can be null, and other parts could have been set to glue
     if (ch) {
-#ifdef SHOW_BORDERS
-      // bounding box of the part
-      aRenderingContext.SetColor(NS_RGB(0,0,0));
-      aRenderingContext.DrawRect(nsRect(dx,start[i],width+30*(i+1),end[i]-start[i]));
-#endif
       dy = offset[i];
-      if (0 == i) { // top
+      if (0 == i) {
         clipRect.SetRect(dx, aRect.y, width, aRect.height);
       }
-      else if (1 == i) { // middle
+      else if (1 == i) {
         clipRect.SetRect(dx, end[0], width, start[2]-end[0]);
       }
-      else { // bottom
+      else {
         clipRect.SetRect(dx, start[2], width, end[2]-start[2]);
       }
       if (!clipRect.IsEmpty()) {
@@ -2101,10 +2078,10 @@ nsMathMLChar::PaintVertically(nsIPresContext*      aPresContext,
         return NS_ERROR_UNEXPECTED;
       }
       // paint the rule between the parts
-      nsRect rule(aRect.x + lbearing, end[first] - onePixel,
-                  rbearing - lbearing, start[last] - end[first] + 2*onePixel);
-      if (!rule.IsEmpty())
-        aRenderingContext.FillRect(rule);
+      aRenderingContext.FillRect(aRect.x + lbearing,
+                                 end[first] - onePixel,
+                                 rbearing - lbearing,
+                                 start[last] - end[first] + 2*onePixel);
       first = last;
       last++;
     }
@@ -2230,13 +2207,13 @@ nsMathMLChar::PaintHorizontally(nsIPresContext*      aPresContext,
                                  end[i] - start[i], bmdata[i].ascent + bmdata[i].descent));
 #endif
       dx = offset[i];
-      if (0 == i) { // left
+      if (0 == i) {
         clipRect.SetRect(dx, aRect.y, aRect.width, aRect.height);
       }
-      else if (1 == i) { // middle
+      else if (1 == i) {
         clipRect.SetRect(end[0], aRect.y, start[2]-end[0], aRect.height);
       }
-      else { // right
+      else {
         clipRect.SetRect(start[2], aRect.y, end[2]-start[2], aRect.height);
       }
       if (!clipRect.IsEmpty()) {
@@ -2279,10 +2256,10 @@ nsMathMLChar::PaintHorizontally(nsIPresContext*      aPresContext,
         return NS_ERROR_UNEXPECTED;
       }
       // paint the rule between the parts
-      nsRect rule(end[first] - onePixel, dy - ascent,
-                  start[last] - end[first] + 2*onePixel, ascent + descent);
-      if (!rule.IsEmpty())
-        aRenderingContext.FillRect(rule);
+      aRenderingContext.FillRect(end[first] - onePixel,
+                                 dy - ascent,
+                                 start[last] - end[first] + 2*onePixel,
+                                 ascent + descent);
       first = last;
       last++;
     }