Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 5877)
+++ /CKEditor/trunk/CHANGES.html	(revision 5878)
@@ -80,4 +80,5 @@
 		<li><a href="http://dev.ckeditor.com/ticket/5353">#5353</a> : wrong width of editor after resize() called in firefox 3.6.</li>
 		<li><a href="http://dev.ckeditor.com/ticket/5778">#5778</a> : [IE] Unwanted scroll on first mouse right-click.</li>
+		<li><a href="http://dev.ckeditor.com/ticket/5218">#5218</a> : [FF] Copy/paste of an image from same domain changed URL to relative URL.</li>
 		<li>Updated the following language files:<ul>
 			<li><a href="http://dev.ckeditor.com/ticket/6246">#6246</a> : Chinese Simplified;</li>
Index: /CKEditor/trunk/_source/plugins/htmldataprocessor/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/htmldataprocessor/plugin.js	(revision 5877)
+++ /CKEditor/trunk/_source/plugins/htmldataprocessor/plugin.js	(revision 5878)
@@ -264,5 +264,6 @@
 	}
 
-	var protectAttributeRegex = /<(?:a|area|img|input)[\s\S]*?\s((?:href|src|name)\s*=\s*(?:(?:"[^"]*")|(?:'[^']*')|(?:[^ "'>]+)))/gi;
+	var protectAttributeRegex = /<((?:a|area|img|input)[\s\S]*?\s)((href|src|name)\s*=\s*(?:(?:"[^"]*")|(?:'[^']*')|(?:[^ "'>]+)))([^>]*)>/gi,
+		findSavedSrcRegex = /\s_cke_saved_src\s*=/;
 
 	var protectElementsRegex = /(?:<style(?=[ >])[^>]*>[\s\S]*<\/style>)|(?:<(:?link|meta|base)[^>]*>)/gi,
@@ -276,5 +277,12 @@
 	function protectAttributes( html )
 	{
-		return html.replace( protectAttributeRegex, '$& _cke_saved_$1' );
+		return html.replace( protectAttributeRegex, function( tag, beginning, fullAttr, attrName, end )
+			{
+				// We should not rewrite the _cke_saved_src attribute (#5218)
+				if ( attrName == 'src' && findSavedSrcRegex.test( tag ) )
+					return tag;
+				else
+					return '<' + beginning + fullAttr + ' _cke_saved_' + fullAttr + end + '>';
+			});
 	}