I'm using the Semantic Grid System to build a responsive site. However, something isn't quite right with the media queries that should obviously kick in once it hits a particular screen size.

I'll reference what i mean with their example on the website : if I view this on my iPhone for example, given that it is supposed to adjust to a single column structure on a mobile device, it still throws out the web version of the page. That is true for both Safari and Chrome on my iPhone. However, if I use the RWD bookmarklet to check it's appearance at different resolutions it appears as expected for the mobile resolution. Also, ironically, if I resize the page in Safari on my desktop it also adjusts accordingly once I get down to the approriate screen size, but not in Firefox.

The media query that it uses once it hits 720px is

@media screen and (max-width: 720px) {
#maincolumn,
#sidebar {
    .column(12);
    margin-bottom: 1em;
}
}

and I might be wide of the mark here but I think that must be the issue. But given that this is directly from the semantic.gs website I'm not inclined to question their own code.

Any idea what the problem might be?