If you are referring to the code in this forum post, then you can add your gallery's configuration options as attributes to the opening <juiceboxgallery > tag.
For example, you could change the line:

echo '<juiceboxgallery galleryTitle="Juicebox Gallery">';

... to something like:

echo '<juiceboxgallery galleryTitle="Juicebox Gallery thumbsPosition="TOP" autoPlayOnLoad="TRUE" captionPosition="BELOW_IMAGE">';

Alternatively, you can set configuration options in the JavaScript embedding code as noted here.

To hide the thumbnails and Thumbnail Button on the Button Bar, set the following:
showThumbsOnLoad="FALSE" ('Customize -> Thumbnails')
showSmallThumbsOnLoad="FALSE" ('Customize -> Thumbnails')
showThumbsButton="FALSE" ('Customize -> Thumbnails')
showSmallThumbsButton="FALSE" ('Customize -> Thumbnails')

To have the slide show start automatically, set:
autoPlayOnLoad="TRUE" ('Customize -> AutoPlay')

You can change the imageTransitionType and imageTransitionTime in the Main Image section and you can set the displayTime in the AutoPlay section.

If you want the slide show to loop continuously, set:
enableLooping="TRUE" ('Customize -> General')

Depending on the dimensions of your gallery and images, you might also want to fill the gallery's image area by setting:
imageScaleMode="FILL" ('Customize -> Main Image')

In order for the automated slide show to display on mobile devices, you could force the gallery to be displayed in Large Screen Mode on all devices and in all browsers by setting:
screenMode="LARGE"  ('Customize -> General')

I am not familiar with concrete5 but you should be able to embed a Juicebox gallery in one of your web pages using the baseUrl method documented here.

For example, if you uploaded a complete gallery folder named 'my_gallery_folder' to the root directory of your web space, then you could embed it in a web page using the following code:

<!--START JUICEBOX EMBED-->
<script src="/my_gallery_folder/jbcore/juicebox.js"></script>
<script>
  new juicebox({
    baseUrl: '/my_gallery_folder/',
    containerId : 'juicebox-container',
    galleryWidth : '100%',
    galleryHeight : '600',
    backgroundColor: '#222222'
  });
  </script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

The leading slash in the paths denotes your root directory so the code above should work in any web page throughout your site.

The dimensions of the image will be determined by Juicebox depending on the size of the gallery and the imageScaleMode chosen but this really only affects the height and width dimensions of the <img> tags. Ultimately, the images are dynamically resized to fill the specified dimensions by the browser whose scaling algorithms cannot be changed.
All that can really be done is change the resolution and/or quality of the images in the gallery to see which settings provide the best results.

Images in a Juicebox-Lite gallery are displayed using standard <img> tags (generated by the gallery's JavaScript code) and are scaled dynamically by the browser (as Juicebox-Lite uses the default value of imageScaleMode="SCALE_DOWN") so how the images look is somewhat dependent on the browser and its own scaling algorithms.
Out of interest, you might like to try using a different browser (Chrome vs Mobile Safari) to see if this makes a difference.
Perhaps the best solution would be to feed Juicebox-Lite larger images with a higher quality.
JuiceboxBuilder-Lite has default settings of 1024 x 768 at 80% quality. Try increasing these values to something like 4096 x 3072 at 90% quality (at least for testing purposes). Even if this produces images which are actually too large for a real-life gallery, if you get better results, it might hint that you would benefit from using larger resolution/higher quality images in your gallery than you currently do.
If you were using JuiceboxBuilder-Pro, I would recommend using a Multi-Size Image gallery.
Essentially, your gallery would contain up to 3 different sizes of images and Juicebox-Pro would use the most appropriate size, depending on the device being used to view the gallery. The Multi-Size Image logic also takes into account factors such as retina screens such as those on iPads.
Please see here for more details.

wspollack is right. There is no way to stack the thumbnails on top of the main image (overlapping it).
The thumbnails can be positioned only using the thumbsPosition configuration option (TOP, BOTTOM, LEFT or RIGHT relative to the main image).
It would not even be possible via CSS. Juicebox would not be aware of any such modification and would expect the thumbnails to be in one of the designated thumbsPosition locations. Trying to change this manually may cause problems when the gallery is redrawn (for example when the browser window is resized).

When thumbnails are hidden (via the Thumbnail Button on the Button Bar), the main image is resized to take advantage of the extra space that has become available.

The best I can suggest is that you post this idea in the Feature Requests forum thread for potential inclusion in a future version.

I use Firefox 38.0.1 on my own PC and I've not had the browser or computer freeze for 15 to 20 seconds whilst loading a page containing a Juicebox gallery (even with a completely cleared cache) so the problem might be unique to your own Firefox browser.
Try temporarily disabling any extensions and plugins that you may have installed in your Firefox browser (via 'Tools -> Add-ons') and then re-enable them, one by one, to see if you can find the source of the problem.
You might also like to try refreshing Firefox by following the instructions here to see if this helps: https://support.mozilla.org/en-US/kb/re … d-settings

Thank you for providing the URL to your web page and the screenshots.

The main problem is most likely with the dimensions of your gallery.
Your gallery has a height of 100% and, if the gallery was the only element on the page, it would fill the height of the browser window. However, your page contains a header and footer and the gallery has no parent container which has been given a height via CSS so Juicebox is unable to determine what its height should be 100% of.
Perhaps the easiest fix for this would be to set your gallery's height to be a fixed pixel value instead (such as 600px).

Also, your web page has a few HTML errors and it might help to fix these. There are not many errors but they may be non-trivial (stray and duplicate Doctype Declartations, <html>, <head> and <body> tags).
You can check the code on your web page with the W3C Markup Validation Service and fix the errors reported.

The gallery title overlapping the thumbnails images is caused by certain CSS rules in your 'style.css' file.
Lines 29-35:

body, input, select, textarea {
    color: #000000;
    font-family: "Raleway", Helvetica, sans-serif;
    font-size: 13pt;
    font-weight: 400;
    line-height: 2em;
}

Lines 328-330:

textarea {
    padding: 0.75em 1em;
}

These CSS rules apply to all 'textarea' tags on your page, including those within the Juicebox gallery. Juicebox has no option but to inherit such global CSS rules.
I would recommend that you apply your custom CSS rules to only those elements on your web page that require them through use of CSS selectors (ids and classes).

With a gallery of fixed height, the HTML errors on your page fixed and custom CSS applied only to non-gallery elements on your page, things should hopefully look better.

Your https://www.countyfairgrounds.net/colorado/config.xml file still contains only 14 image entries.

Either:
(1) The 'config.xml' file is not being overwritten in your gallery folder when you edit the gallery with JuiceboxBuilder-Pro.
... or:
(2) The 'config.xml' file is not being overwritten on your web server.

Double-check that your new 'config.xml' file contains 15 image entries (you can open the file in a plain text editor).
If it contains only 14 image entries, then the file is not being overwritten. Check that your gallery folder is not read-only and that you do not have any gallery files open in any applications (other than JuiceboxBuilder-Pro) when you save the gallery on the 'Publish' tab. You could also try saving the new version of the gallery to a completely different folder.

If you are in any doubt that the old 'config.xml' file is being overwritten on your web server, delete it first before uploading the new version in its place.

Also, be sure to upload the new image and thumbnail to the gallery's 'images' and 'thumbs' folders.

After editing a gallery with JuiceboxBuilder-Pro, you should be able to just upload the entire gallery folder to your web server without having to manually pick out any specific files.
If you use a dedicated FTP program such as Filezilla, you could upload the entire gallery folder to your web server (to replace the old version) in a single drag-and-drop action and configure the FTP program to upload only new or updated files (to avoid having to re-upload images that already exist on the server).

It sounds like you have added the new image to the SEO code in your HTML page (the page which contains the gallery's embedding code). This code is used only to help search engines index the content in your gallery. Please see here for more information.
The list of images which Juicebox displays in the gallery is stored in the gallery's 'config.xml' file.
Once you have updated a gallery in JuiceboxBuilder-Pro (to add or remove images), just upload the new 'config.xml' file to your web server, replacing the existing one (and clear your browser's cache after doing so to make sure that your browser uses the most recent version).

@NeillTaylor

When I click the Facebook share icon in your gallery, the correct image (the og:image) is being used in the pop-up window.
It sounds like Facebook (or your browser) may have been using an older, cached version of your web page.

Just for good measure, try clearing Facebook's own cache of your web page (so that the new image is used) by entering your web page's URL into Facebook's Open Graph Debugger.
Also, clear your browser's cache before reloading your web page.

Hopefully this will help.

Incidentally, the shareURL is used only by JuiceboxBuilder-Pro (and not by Juicebox-Pro itself when the gallery is displayed) to know what URL to use when populating the Open Graph tags in the index page when the gallery is created.