Fix bug in FF on enter.

source/Editor.js

@@ -1002,6 +1002,8 @@ document.addEventListener( 'DOMContentLoaded', function () {
                 splitTag = nextTag[ tag ],
                 nodeAfterSplit;
             
+            // If this is a malformed bit of document, just play it safe
+            // and insert a <br>.
             if ( !block ) {
                 range._insertNode( createElement( 'BR' ) );
                 range.collapse( false );

source/Node.js

@@ -107,6 +107,8 @@ implement( Text, {
     getLength: function () {
         return this.length;
     },
+    // The text node is essentially its own contents.
+    empty: function () { return this; },
     isLike: function ( node ) {
         return node.nodeType === TEXT_NODE;
     },