--- a/calendar/lightning/modules/ltnInvitationUtils.jsm
+++ b/calendar/lightning/modules/ltnInvitationUtils.jsm
@@ -292,17 +292,17 @@ ltn.invitation = {
          * @param {Node}    aToNode text node to change
          * @param {String}  aType   use 'newline' for the same, 'added' or 'removed' for decoration
          * @param {String}  aText   [optional]
          * @param {Boolean} aClear  [optional] for consecutive changes on the same node, set to false
          */
         function _content2Child(aToNode, aType, aText = "", aClear = true) {
             let nodeDoc = aToNode.ownerDocument;
             if (aClear && aToNode.hasChildNodes()) {
-                aToNode.removeChild(aToNode.firstChild);
+                aToNode.firstChild.remove();
             }
             let n = nodeDoc.createElement(aType.toLowerCase() == "newline" ? "br" : "span");
             switch (aType) {
                 case "added":
                 case "modified":
                 case "removed":
                     n.className = aType;
                     if (Preferences.get("calendar.view.useSystemColors", false)) {