Form's legend overlay fieldset border in Firefox 57.0 x64

[maksimkanev]

Text from Form's Fieldset border is shown under the Legend in Firefox 57.0 x64

<div class="row">
  <div class="col col-6 push-center">
    <form class="form" #loginForm="ngForm" (ngSubmit)="onSubmit()">
      <fieldset>
        <legend>Login data</legend>
        <div class="form-item">
          <label for="username">Username</label>
          <input type="text" name="username" id="username"
                 required="required"
                 [(ngModel)]="username"/>
        </div>
        <div class="form-item">
          <label for="password">Password</label>
          <input type="password" name="password" id="password"
                 required="required"
                 [(ngModel)]="password"/>
        </div>
        <div class="form-item">
          <button type="submit">Login</button>
        </div>
      </fieldset>
    </form>
    <div class="message error" data-component="message"
         *ngIf="authStatus=='failed'">Username or password is invalid<span class="close small"></span></div>
  </div>
</div>