fix for #38834 r=ben (last week sometime)

make wizard page X of Y localizable

xpfe/global/resources/content/wizardManager.js

@@ -157,14 +157,14 @@ function WM_ProgressUpdate( currentPageNumber )
 {
   var statusbar = document.getElementById ( "status" );
   if ( statusbar ) {
-    var string = "";
-    string += (currentPageNumber + 1);
-    try {
-      string += ( " " + this.bundle.GetStringFromName("oflabel") + " " );
-    } catch (e) {
-      // mac string bundle hack
-      string += " of ";
-    }
+      var string;
+      try {
+          string = this.bundle.formatStringFromName("oflabel",
+                                                    [currentPageNumber,
+                                                    this.GetMapLength], 2);
+      } catch (e) {
+          string = "";
+      }
     string += this.GetMapLength();
     statusbar.setAttribute( "progress", string );
   }

xpfe/global/resources/locale/en-US/wizardManager.properties

@@ -1,3 +1,3 @@
 finishButtonLabel=Finish
 nextButtonLabel=Next
-oflabel=of
+oflabel=%S of %S