Landing pull request 352. Slightly improved defaultDisplay() and Throbber of Doom. Fixes #8994.

More Details:
 - https://github.com/jquery/jquery/pull/352
 - http://bugs.jquery.com/ticket/8994

src/effects.js

@@ -574,7 +574,8 @@ function defaultDisplay( nodeName ) {
 
 	if ( !elemdisplay[ nodeName ] ) {
 
-		var elem = jQuery( "<" + nodeName + ">" ).appendTo( "body" ),
+		var body = document.body,
+			elem = jQuery( "<" + nodeName + ">" ).appendTo( body ),
 			display = elem.css( "display" );
 
 		elem.remove();
@@ -588,14 +589,15 @@ function defaultDisplay( nodeName ) {
 				iframe.frameBorder = iframe.width = iframe.height = 0;
 			}
 
-			document.body.appendChild( iframe );
+			body.appendChild( iframe );
 
 			// Create a cacheable copy of the iframe document on first call.
-			// IE and Opera will allow us to reuse the iframeDoc without re-writing the fake html
-			// document to it, Webkit & Firefox won't allow reusing the iframe document
+			// IE and Opera will allow us to reuse the iframeDoc without re-writing the fake HTML
+			// document to it; WebKit & Firefox won't allow reusing the iframe document.
 			if ( !iframeDoc || !iframe.createElement ) {
 				iframeDoc = ( iframe.contentWindow || iframe.contentDocument ).document;
-				iframeDoc.write( "<!doctype><html><body></body></html>" );
+				iframeDoc.write( ( document.compatMode === "CSS1Compat" ? "<!doctype html>" : "" ) + "<html><body>" );
+				iframeDoc.close();
 			}
 
 			elem = iframeDoc.createElement( nodeName );
@@ -604,7 +606,7 @@ function defaultDisplay( nodeName ) {
 
 			display = jQuery.css( elem, "display" );
 
-			document.body.removeChild( iframe );
+			body.removeChild( iframe );
 		}
 
 		// Store the correct default display