CSS media query not recognized by Firefox browser

This URL looks fine in Safari and Chrome, but not in Firefox:
http://www.southviewcemetery.com

Specifically, in Firefox there are two logos displaying at full screen size (over 1144px wide), in addition to a few other formatting problems. I have several elements setup with a class "mobileonly" that should not be displaying:

ul#nav1 li.mobileonly{display:none;}
.mobileonly{display:none;}

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HTML:

<div id="mobilespacer" class="mobileonly"><a href="default.asp"><img id="mobilelogo" class="mobileonly" src="img/lg_southview-resp.png" /></a><img id="mobilenav" src="img/gr_mobilenav.jpg" /></div>

<ul id="nav1">
	<li class="mobileonly"><a href="about-us.asp">Home</a></li>
	<li><a href="about-us.asp">About Us</a></li>
	<li><a href="pre-planning.asp">Pre-Planning</a></li>
	<li><a href="burial-arrangements.asp">Burial Arrangements</a></li>
	<li><a href="markers-and-flowers.asp">Markers &amp; Flowers</a></li>
	<li><a href="our-history.asp">Our History</a></li>
</ul>

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I've gone through my code several times, I can't find what is wrong. Would appreciate another set of eyes.

Thank you!