See https://bugzilla.mozilla.org/show_bug.cgi?id=1735738 for reference.
if (this.output.insertAdjacentHTML) {
        
        this.output.insertAdjacentHTML("BeforeEnd", message);
      } else {
        this.output.textContent += message;
      }
      if (message.lastIndexOf("\n") >= 0 && !this.disableScrolling.checked) {
        
        this.output.scrollTop = this.output.scrollHeight;
      }
    },
    _done: function Driver_done() {
      if (this.inFlightRequests > 0) {
        this.inflight.textContent = this.inFlightRequests;
        setTimeout(this._done.bind(this), WAITING_TIME);
      } else {
        setTimeout(this._quit.bind(this), WAITING_TIME);
      }
    },
    _sendResult: function Driver_sendResult(snapshot, task, failure, callback) {
      var result = JSON.stringify({
        browser: this.browser,
        id: task.id,
        numPages: task.pdfDoc ? task.lastPage || task.pdfDoc.numPages : 0,
        lastPageNum: this._getLastPageNumber(task),
        failure,
        file: task.file,
        round: task.round,
        page: task.pageNum,
        snapshot,