Flexbox not working properly on Firefox but okay on Chrome & Safari

Question

I'm building a website that relies heavily on flexbox. Only problem is that I cannot get it to mimic the chrome behaviour on Firefox. I looked on CSS-Tricks, SO and at this article (http://philipwalton.com/articles/normalizing-cross-browser-flexbox-bugs/)

All these were very nice and gave some good suggestions, none of which worked for me. I tried setting

* {
    min-height: 0;
    min-width: 0;
}

And every variation on my child and parent elements, but to no avail. I have included a CodePen link that illustrates my problem. When opened in FF 37.0.2 AND 46.0.1, it is completely broken. In Chrome and Safari, it looks just fine.

/*  Header Styles  */

#header{
    width:85%;
    margin:0 auto;
    height:375px;
    background-color:rgba(252,241,223, 1);
    padding:25px 75px 25px 0;
    font-family: 'Quattrocento Sans', sans-serif;
    border-radius:3px 3px 0 0;
}


#header-logo{
    width:33%;
    height:100%;
    display:flex;
    display: -webkit-box;      /* OLD - iOS 6-, Safari 3.1-6 */
    display: -moz-box;         /* OLD - Firefox 19- (buggy but mostly works) */
    display: -ms-flexbox;      /* TWEENER - IE 10 */
    display: -webkit-flex;     /* NEW - Chrome */
    align-items:center;
    justify-content:center;
    float:left;
}

#header-nav{
    width:66%;
    height:100%;
    display:flex;
    display: -webkit-box;      /* OLD - iOS 6-, Safari 3.1-6 */
    display: -moz-box;         /* OLD - Firefox 19- (buggy but mostly works) */
    display: -ms-flexbox;      /* TWEENER - IE 10 */
    display: -webkit-flex;     /* NEW - Chrome */
    justify-content:center;
/*  align-items:center;*/
    flex-direction:column;
}
#header-nav-tabs{
    margin-top:25px;
    padding-top:25px;
    border-top:1px solid rgba(0,0,0,0.5);
}

#header-nav-tabs a{
    font-size: 20px;
    color:black;
    text-decoration:none;
    margin:0 10px;
    white-space: nowrap;
}

#header-nav-tabs a:hover{
    text-decoration:underline;
}


@media screen and (max-width: 680px) {

    #header{
        height:auto;
        text-align:center;
        padding:25px;
        display:flex;
        display: -webkit-box;      /* OLD - iOS 6-, Safari 3.1-6 */
        display: -moz-box;         /* OLD - Firefox 19- (buggy but mostly works) */
        display: -ms-flexbox;      /* TWEENER - IE 10 */
        display: -webkit-flex;     /* NEW - Chrome */
        flex-direction: column;
        align-items: center;
    }

    #header-logo{
        width:auto;
        height:auto;
    }

    #header-nav{
        width:auto;
        height:auto;
    }

    #header-nav-tabs a{
        font-size:17px;
    }


}

<header id="header" role="banner">
<div id="header-logo">
    <img src="http://staging.thestarvingsailor.ca/wp-content/uploads/2016/01/Moore-Logo.png" />
</div>

<div id="header-nav">

    <div id="header-nav-title">
        <h1>Test Site</h1>
        <p>Description for the test site.</p>
    </div>

    <div id="header-nav-tabs">
        <a href="http://www.moorefamilychiropractic.ca">Home</a>
        <a href="http://www.moorefamilychiropractic.ca/about-us">About Us</a>
        <a href="http://www.moorefamilychiropractic.ca/services">Services</a>
        <a href="http://www.moorefamilychiropractic.ca/reviews">Reviews</a>
        <a href="http://www.moorefamilychiropractic.ca/blog">Blog</a>
        <a href="http://www.chirocorrection.com/moorechiro/" target="_blank" rel="noopener noreferrer">My ChiroCorrection</a>
        <a href="http://www.moorefamilychiropractic.ca/how-can-chiropractic-help-me">How Can Chiropractic Help Me?</a>
        <a href="http://www.moorefamilychiropractic.ca/contact-us">Contact Us</a>
    </div>

</div>
</header>

http://codepen.io/anon/pen/mPYZGY

Answer 1

Try changing the order of the display property declarations such that the standard is last. I think FF is letting that -moz prefixed property overwrite the previously declared value(s).

display: -webkit-box;      /* OLD - iOS 6-, Safari 3.1-6 */
display: -moz-box;         /* OLD - Firefox 19- (buggy but mostly works) */
display: -ms-flexbox;      /* TWEENER - IE 10 */
display: -webkit-flex;     /* NEW - Chrome */
display:flex;

Answer 2

The problem is the order of your prefixes.

Always put the official property (W3C standard) last in the list.

The CSS rendering engine will select the last applicable property. Firefox is reading past display: flex and selecting display: -moz-box, which is causing the problem.

More details: What is the proper way to order vendor prefixes for flexbox?