(Re) Fixes #8884 in a way that keeps the format of the headers map sent to transports natural.

src/ajax.js

@@ -95,7 +95,7 @@ function addToPrefiltersOrTransports( structure ) {
 	};
 }
 
-//Base inspection function for prefilters and transports
+// Base inspection function for prefilters and transports
 function inspectPrefiltersOrTransports( structure, options, originalOptions, jqXHR,
 		dataType /* internal */, inspected /* internal */ ) {
 
@@ -389,6 +389,7 @@ jQuery.extend({
 			ifModifiedKey,
 			// Headers (they are sent all at once)
 			requestHeaders = {},
+			requestHeadersNames = {},
 			// Response headers
 			responseHeadersString,
 			responseHeaders,
@@ -412,7 +413,9 @@ jQuery.extend({
 				// Caches the header
 				setRequestHeader: function( name, value ) {
 					if ( !state ) {
-						requestHeaders[ name.toLowerCase() ] = { n: name, v: value };
+						var lname = name.toLowerCase();
+						name = requestHeadersNames[ lname ] = requestHeadersNames[ lname ] || name;
+						requestHeaders[ name ] = value;
 					}
 					return this;
 				},

src/ajax/xhr.js

@@ -104,7 +104,7 @@ if ( jQuery.support.ajax ) {
 					// Need an extra try/catch for cross domain requests in Firefox 3
 					try {
 						for ( i in headers ) {
-							xhr.setRequestHeader( headers[ i ].n, headers[ i ].v );
+							xhr.setRequestHeader( i, headers[ i ] );
 						}
 					} catch( _ ) {}