Index: mu-plugins/jetpack-tweaks.php
===================================================================
--- mu-plugins/jetpack-tweaks.php	(revision 2648)
+++ mu-plugins/jetpack-tweaks.php	(working copy)
@@ -201,7 +201,7 @@
  */
 function sanitize_urls_in_css_properties( $url, $property ) {
 	$allowed_properties = array( 'background', 'background-image', 'border-image', 'content', 'cursor', 'list-style', 'list-style-image' );
-	$allowed_protocols  = array( 'http', 'https' );
+	$allowed_protocols  = array( 'http', 'https', 'data' );
 
 	// Clean up the string
 	$url = trim( $url, "' \" \r \n" );