On a Mac, all you should need to do is extract the 'juicebox_lite_1.5.0.zip' file, go inside the 'juicebox_lite_1.5.0/adobe-lightroom-plugin/' folder and double-click the 'juicebox_lite.lrwebengine' package.
If this does not work, then it might be worthwhile uninstalling and then reinstalling Adobe Lightroom to see if this helps (although the manual method of copying the 'juicebox_lite.lrwebengine' package to the 'Web Galleries' folder should also work fine).
Also, please make sure that you have Adobe Lightroom v4 or later installed. The 'juicebox_lite.lrwebengine' plugin will not work with Adobe Lightroom v3 or earlier.

If you cannot find Adobe Lightroom's 'Web Galleries' folder on your computer, then please try the suggestion from my post above:

• Open Lightroom

• Go to 'Edit -> Preferences...' (from the drop-down menu at the top)

• Select the 'Presets' tab

• Click the 'Show Lightroom Presets Folder...' button

• Navigate inside the 'Lightroom' folder in the file explorer window that pops up

• Now navigate inside the 'Web Galleries' folder

This is the folder that you should copy and paste the 'juicebox_lite.lrwebengine' package to (when installing the plugin manually if double-clicking the 'juicebox_lite.lrwebengine' package does not work).
If you do not have a 'Web Galleries' folder (although it should exist by default after installing Lightroom), then try creating it manually in your 'Users/username/Library/Application Support/Adobe/Lightroom/' directory.

There should be no need to look inside the package (although it seems strange that you do not see anything inside it).
To install the plugin to Adobe Lightroom, either double-click the 'juicebox_lite.lrwebengine' package or, if this does not work, copy and paste the 'juicebox_lite.lrwebengine' package to the 'Web Galleries' folder (see above).

The 'juicebox_lite.lrwebengine' package is bundled within the Juicebox-Lite zip file.
Extract the 'juicebox_lite_1.5.0.zip' file and you'll find the 'juicebox_lite.lrwebengine' package in this location: juicebox_lite_1.5.0/adobe-lightroom-plugin/juicebox_lite.lrwebengine

The only location that the plugin should be installed to is 'Users/username/Library/Application Support/Adobe/Lightroom/Web Galleries/'.

Sorry. There was an instance of 'juicebox_pro.lrwebengine' rather than 'juicebox_lite.lrwebengine' in my post above (which I have since corrected).

I hope these notes help you to successfully install the plugin.

Edit:
Incidentally, the Lightroom plugin was first bundled into the Juicebox-Lite zip file in v1.4.3.
If you have a version prior to v1.4.3, you will not find the 'juicebox_lite.lrwebengine' package inside the Juicebox-Lite zip file.
You can download the current version of Juicebox-Lite (v1.5.0) from the download page here.

When a Juicebox gallery is displayed on a touch-enabled mobile device, Juicebox uses Touch Input Mode (rather than Mouse Input Mode). Please see the Input Mode support section for more information.

In Touch Input Mode, the imageTransitionType is always set to SLIDE (which is the transition which best fits with the swipe gesture for navigating between images).
The imageTransitionType can be set only for Large Screen Mode and Mouse Input Mode. This is noted in the short description for imageTransitionType in the Main Image section of the Config Options Page:

Unfortunately, there is no way to change the imageTransitionType on a touch-enabled mobile device. It will always be set to SLIDE.

However, if you like, you can post suggestions for future versions in the Feature Requests forum thread.
This keeps all the ideas together and ensures that they are not overlooked by the developers.
I do not know the likelihood of any suggestions being implemented but this is certainly the best place for all ideas.
Thank you.

There are a few factors which determine how Juicebox-Pro displays a gallery.

First of all, thumbnails and main images are displayed on separate pages only in Small Screen Mode. In Large Screen Mode, the thumbnails and main images are displayed together on the same page.
By default, Juicebox-Pro will use Small Screen Mode only on mobile (small screen) devices.
If you want Juicebox-Pro to always use Small Screen Mode regardless of the device being used to view the gallery (and, therefore, always display thumbnails on a separate page), set screenMode="SMALL" (in JuiceboxBuilder-Pro's 'Customize -> General' section).

To ensure that the thumbnail page is displayed (rather than the first image in the gallery) when the gallery is initially loaded, be sure to set showSmallThumbsOnLoad="TRUE" (in JuiceboxBuilder-Pro's 'Customize -> Thumbnails' section).

In Small Screen Mode, if a gallery is displayed on a page of its own (with dimensions of 100% x 100% and no other content on the page), then the thumbnail page will be displayed by default.
However, if the gallery is embedded in a page (with dimensions of less than 100% x 100% or with other content on the page), then the Splash Page will be used by default. (The user can click/tap the Splash Page to expand the gallery.)
To disable the Splash Page and always display the thumbnail page (regardless of whether the gallery is embedded alongside other content or not), set showSplashPage="NEVER" (in JuiceboxBuilder-Pro's 'Customize -> Splash Page' section).

Please note that the actual number of thumbnails displayed will depend on the thumbnail dimensions (thumbWidth and thumbHeight) and the available space on the user's screen. If there is not enough room to display all teh thumbnails in the gallery, then additional thumbnail pages will be generated and the user can navigate through them by swiping left and right (in Touch Input Mode) or by clicking the thumbnail paging arrows (in Mouse Input Mode).

More information about Screen Modes, Input Modes and the Splash Page can be found in the Gallery Tour.

I hope this helps to clarify things.
Setting screenMode="SMALL" will be enough for Juicebox-Pro to use separate thumbnail pages but, depending on other factors (see above), it might not be enough for the thumbnail pages to initially be displayed. You might find that you need to also set showSmallThumbsOnLoad="TRUE" and showSplashPage="NEVER".

If you continue to experience difficulties, please post the URL to your gallery's web page so that I can take a look at your gallery for myself and hopefully help further. Thank you.

You're welcome!
I'm glad that my suggestion was useful.

The 'full.html' file is used internally by Juicebox when a gallery is expanded (via the Splash Page or the Button Bar's Expand Button) on a page of its own (i.e. when expandInNewPage="TRUE" or on iOS devices) rather than on top of the embedding page.
As such, the 'full.html' file should be left as it is and should not be modified.
(Please see the Expand Gallery Behavior support section for further information.)

Set showSplashPage="NEVER" in JuiceboxBuilder-Pro's 'Customize -> Splash Page' section (and showSmallThumbsOnLoad="TRUE" in the 'Customize -> Thumbnails' section) and, in Small Screen Mode, Juicebox-Pro will initially display the thumbnail page instead of the Splash Page. (In Large Screen Mode, Juicebox-Pro will not display the Splash Page unless showSplashPage="ALWAYS" so setting showSplashPage="NEVER" will not make any difference to the Large Screen Mode display.)

You're welcome! I'm glad we've been able to help with your queries.

That's great!
Thank you for letting me know.

Here are a few suggestions which might help.

(1) Try completely clearing your browser's cache before reloading your gallery's web page to see if this helps.
(2) Try viewing your gallery in different browsers (Chrome, Edge, Firefox, Internet Explorer, Opera, Safari) on your desktop computer to see if the problem is unique to a certain browser.
(3) If you have any browser extensions installed (like an ad blocker for example), try temporarily disabling them to see if this makes a difference.
(4) Try upgrading your gallery to the current version of Juicebox-Pro (v1.5.0). You can download the latest version using the link from your purchase email. Just swap your gallery's 'jbcore' folder for the one inside the Juicebox-Pro v1.5.0 zip package ('juicebox_pro_1.5.0/web/jbcore/'). Full instructions for downloading the latest version and upgrading existing galleries can be found on the Upgrading Juicebox support page.
(5) If you continue to experience difficulties, please post the URL to your gallery's web page so that I can take a look at the gallery for myself. I might see something that helps to determine the cause of your problem. Thank you.

You're welcome!

Try this 'wp-juicebox.php' file.
It should hopefully work fine as a replacement for the 'wp-juicebox.php' file from the current version of WP-Juicebox (v1.5.0).
However, please remember that this is not an official solution and you should use the file at your own risk. The code was provided by a member of the forum community and it has not been extensively tested with v1.5.0.

You could try something like the following:

<!--START JUICEBOX EMBED-->
<script src="jbcore/juicebox.js"></script>
<script>
    var jb = new juicebox({
        containerId: 'juicebox-container',
        galleryWidth: '100%',
        galleryHeight: '100%',
        backgroundColor: '#222222',
        backButtonPosition: 'TOP',
        backButtonText: '',
        backButtonURL: 'http://www.example.com/index.html',
        useFullscreenExpand: 'TRUE'
    });
    jb.onInitComplete = function() {
        var filename = (window.devicePixelRatio >= 2) ? 'large.jpg' : 'small.jpg';
        $('.jb-go-back-text').html('<img src="' + filename + '" width="100" height="75" />');
    };
    jb.onExpand = function(expanded) {
        if (expanded) {
            window.setTimeout(function() {
                var filename = (window.devicePixelRatio >= 2) ? 'large.jpg' : 'small.jpg';
                $('.jb-go-back-text').html('<img src="' + filename + '" width="100" height="75" />');
            }, 500);
        }
    };
</script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

The new part is the jb.onExpand code. You could restructure the code to make it more efficient and avoid duplication but I've just left it as it is (with the new code being just a separate addition to the code from my post above) so that's it's easy to follow.
Unfortunately, a short delay is required to ensure that the Back Button is present in the DOM (Document Object Model) before actions are performed on the CSS class after the gallery has been expanded.
The code is starting to get a little messy. This is one of the drawbacks of trying to do something with Juicebox that it was not designed to do. You tend to run into unforeseen problems and have to deal with them as your encounter them.

I would probably be inclined to do this myself. For the sake of a handful of kilobytes, the code would be cleaner and it should work in all scenarios without any further tweaking.
Just use a backButtonText entry such as the following (making sure that the display width and height are both half the actual dimensions of the image).

backButtonText="<img src="http://www.tonyhallphoto.com/jbresources/logo-backbutton-200x50.png" style="width: 100px; height: 25px; margin-top:-5px;" />"

In a Multi-Size Image gallery, 'Large' images are not currently displayed in high pixel density Windows desktop monitors but this has been logged as a bug and should hopefully be fixed in the next version of Juicebox.

Running the 'JuiceboxBuilder-Pro.air' installation file cannot (and will not) install the Lightroom plugin.
The two are completely unrelated (as far as installation code goes).
Please try again. Afterwards, you can check your version of JuiceboxBuilder-Pro from 'Help -> About JuiceboxBuilder-Pro...' from the drop-down menu at the top.

To upgrade JuiceboxBuilder-Pro, run the 'JuiceboxBuilder-Pro.air' installation file (from inside the Juicebox-Pro v1.5.0 zip package): juicebox_pro_1.5.0/JuiceboxBuilder-Pro.air
If you are having problems installing JuiceboxBuilder-Pro, try uninstalling your older version (v1.4.1) first.
For reference, the JuiceboxBuilder-Pro User Guide can be found here.

For anyone interested, instructions for installing the Lightroom plugin can be found on the plugin's support page.

If using the Lightroom plugin to create a gallery that you want to embed, you can grab the necessary embedding code from the gallery's 'index.html' file (which you can open in a plain text editor to view its contents).
Otherwise, you can just use the generic embedding code found in the Embedding Guide and just change the gallery dimensions and background color as necessary.

I hope this helps.

I'm not sure it would be wise to change the default image size for Picasa Web Album galleries.
If this setting was changed from 1600 to 1920, then this would affect all existing WP-Juicebox galleries using a Picasa Web Album as a source of images.
Other users may not want their existing galleries to be changed (to load larger images) by simply upgrading the WP-Juicebox plugin.

Also, Google seems to be slowing discontinuing support for the Picasa Web API. Existing galleries (created prior to Google acquiring Picasa) still display fine but new galleries (created or modified since the acquisition) can no longer be accessed via the API.

Therefore, I think it is unlikely that any new features will be added to WP-Juicebox with regard to the Picasa Web Album functionality.

However, changing the default image size is a quick and easy task (changing a single number in one file) for anyone who wants to do so.

Having said that, please feel free to post suggestions for future versions in the Feature Requests forum thread.
This keeps all ideas together and ensures that they are not overlooked by the developers.
Thank you.