Website showing mobile version in Firefox and Opera

[xoggoth]

IGNORE - PROBLEM SORTED BY MY LITTLE PUPPET PARROT

Got alternate desktop/mobile versions using following line in header:

<link rel="alternate" media="only screen and (max-width: 740px)" href="https://www.gatekeeperel.co.uk/mobile/" >

All works fine on desktop in Chrome, Edge and Brave but in Firefox and Opera I am now seeing the mobile version. Any ideas? Cheers.

PS If you try the site listed note it is not usually slow like that, got some other problem going on at moment.

[xoggoth]

Ah, that is not the problem. I have lines further down to allow for user choice buttons:

<!--go to mobile site if screen too small unless desktop requested-->
<script type="text/javascript">
<?php
if ( !isset($_GET['view']) || $_GET['view']!="desktop" )
{
echo "if (screen.width < 740) document.location = 'mobile/';";
}
?>
</script>

Put in
echo "alert(screen.width);";

and it says the screen width is 20!!!
WTF??????????????

[xoggoth]

Solved. window.screen.width instead of screen.width sorts it. Just screen.width is fine in other browsers and was in Firefox.