If you have an iframe with fixed dimensions, then the iframe will be displayed at those dimensions in all browsers and on all devices.
You could certainly try using percentage dimensions for your iframe (as penum suggests above) but if the iframe is nested within any parent containers with fixed dimensions, then the iframe's own dimensions will become fixed, e.g. 100% x 800px = 800px.
You might like to take a look at this forum thread, entitled "How to get an IFrame to be responsive in iOS Safari?". Although you have a Windows mobile device, the principles will be the same and it might help with your problem. http://stackoverflow.com/questions/2308 … ios-safari
Another thing you might like to try is to use JavaScript to listen for a change in the user's browser window size and then assign new dimensions to your iframe accordingly.
There are examples of this technique in the Using a Resizable Gallery with a Header support section. In the online examples, JavaScript is used to dynamically set the gallery's dimensions. You could copy and modify the code as required to set your iframe's dimensions instead.
Also, as you have already uploaded your complete gallery folder to your web server, you might like to consider embedding your gallery directly on your page (using the baseUrl method as documented here) rather than using an iframe.
You could replace your iframe code with something like the following:
<!--START JUICEBOX EMBED-->
<script src="/gallery/welcome/jbcore/juicebox.js"></script>
<script>
new juicebox({
baseUrl: '/gallery/welcome/',
containerId : 'juicebox-container',
galleryWidth : '100%',
galleryHeight : '600',
backgroundColor: '#222222'
});
</script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->
Just doing this and setting your gallery's width to 100% (so that it fills the width of its parent container), might be enough to solve your problem.