Index: typo3/sysext/backend/Classes/Form/Element/InlineElement.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- typo3/sysext/backend/Classes/Form/Element/InlineElement.php	(revision )
+++ typo3/sysext/backend/Classes/Form/Element/InlineElement.php	(revision )
@@ -1390,7 +1390,7 @@
 				$selectorConfiguration['PA']['fieldConf']['config']['appearance']['elementBrowserAllowed'],
 				TRUE
 			);
-			if (!in_array($fileRecord['extension'], $allowedFileExtensions, TRUE)) {
+			if (!in_array(strtolower($fileRecord['extension']), $allowedFileExtensions, TRUE)) {
 				return FALSE;
 			}
 		}