message: Fix Firefox composer regression exception
diff: @@ -162,10 +162,10 @@ export function renderModel(editor: HTMLDivElement, model: EditorModel) {
  lines.forEach((parts, i) => {
  // find first (and remove anything else) div without className
  // (as browsers insert these in contenteditable) line container
  - let lineContainer = editor.children[i];
  - while (lineContainer && (lineContainer.tagName !== "DIV" || !!lineContainer.className)) {
  + let lineContainer = editor.childNodes[i];
  + while (lineContainer && ((<Element>lineContainer).tagName !== "DIV" || !!(<Element>lineContainer).className)) {
  editor.removeChild(lineContainer);
  - lineContainer = editor.children[i];
  + lineContainer = editor.childNodes[i];
  }
  if (!lineContainer) {
  lineContainer = document.createElement("div");
  