title: Exec --no-startup-id <command> says "--" invalid option
body: <p>I'm trying to launch applications without "wait cursor", according to <a href="https://i3wm.org/docs/userguide.html#_automatically_starting_applications_on_i3_startup" rel="nofollow">i3 userguide</a> I should use <code>--no-statrup-id</code> option of exec but it gives me "impossible" error.</p>
  
  <pre><code>$ exec --no-startup-id firefox
  bash: exec: --: invalid option
  exec: usage: exec [-cl] [-a name] [command [arguments ...]] [redirection ...]
  </code></pre>
  
  <p>Can anybody explain to me what's wrong? In every manual, I find that people use this flag, but <code>man exec</code> have no information about this feature.</p>