Merged revision 42430 from trunk:

Editor: ensure there is a selection before getting the caret position. Fixes a bug in Firefox when there is no selection for a hidden element.

Props johnschulz, azaozz.

Fixes #43012 for 4.9.2.

Built from https://develop.svn.wordpress.org/branches/4.9@42442


git-svn-id: http://core.svn.wordpress.org/branches/4.9@42272 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/editor.js

@@ -695,10 +695,10 @@ window.wp = window.wp || {};
 		 */
 		function findBookmarkedPosition( editor ) {
 			// Get the TinyMCE `window` reference, since we need to access the raw selection.
-			var TinyMCEWIndow = editor.getWin(),
-				selection = TinyMCEWIndow.getSelection();
+			var TinyMCEWindow = editor.getWin(),
+				selection = TinyMCEWindow.getSelection();
 
-			if ( selection.rangeCount <= 0 ) {
+			if ( ! selection || selection.rangeCount < 1 ) {
 				// no selection, no need to continue.
 				return;
 			}