How to enable autocomplete tag in Firefox37

I need to make autocomplete attribute work for my site.However Firefox 37 does not work well as expected. My tag is as below.

<div>
    <label>UserName</label>
    <input type="text" style="display:none" />
    <input type="text" name="UserName" id="UserName" size="20" maxlength="16" autocomplete="off"/>

    <label>Password</label>
    <input type="password" style="display:none" />
    <input type="password" maxlength="4" name="Password" id="Password" autocomplete="off" />
</div>