You can set a URL for the Back Button via the backButtonUrl configuration option (in JuiceboxBuilder-Pro's 'Customize -> Back Button' section).
The URL can be a relative path (relative to the web page containing the gallery's embedding code) or an absolute path (such as http://www.example.com/index.html).

Just set backButtonUrl="http://www.fobgfc.org/?page=gallery" and all should be well.

For reference a list of all Back Button configuration options can be found here.

Many thanks for the details.
As I noted previously, the internal browser within Messenger is not a supported browser so if you share any links to Juicebox galleries within Messenger, it might be worth adding a note along with the link saying something like "For best results, please view in Safari or Chrome."

However, I am very grateful for the extra information that you have provided and I have passed it on to the developers.
Thank you for reporting this issue.

(1) Enter your gallery's baseUrl embedding code into a 'Formatting -> Custom HTML' Gutenberg block.

(2) Upload your gallery folder to your root directory and use a leading slash in your embedding code paths to denote your root directory. This should work with any permalink structure. For example:

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

I hope this helps.

You're welcome!
I'm glad to hear that you have found the cause of your problem.
Thank you for letting me know.

@ctjean

That's certainly the best way to incorporate videos into a Juicebox gallery (to use a gallery image as a link to a corresponding video).
Thank you for sharing your technique!

For others wishing to try this, the linkURL (the link to the video) will be opened when the 'Open Image' button on the gallery's Button Bar is clicked (when setting showOpenButton="TRUE" in JuiceboxBuilder-Pro's 'Customize -> Lite' section) or when the main image itself is clicked (when setting imageClickMode="OPEN_URL" in JuiceboxBuilder-Pro's 'Customize -> Main Image' section).

What you are describing here is the Splash Page.
The Splash Page is an image placeholder for the gallery which, when clicked, expands the gallery to fill the browser window.
The Splash page is displayed by default when the gallery is embedded in a web page alongside other content and displayed in Small Screen Mode (on mobile devices or when screenMode="SMALL"). The Splash Page can also be displayed by setting showSplashPage="ALWAYS".
Please see the Gallery Tour for more information about the Splash Page and Screen Modes.

If you are seeing the Splash Page in a desktop browser, then please ensure the following:
(1) Set screenMode="AUTO" (in JuiceboxBuilder-Pro's 'Customize -> General' section).
(2) Set showSplashPage="AUTO" (in JuiceboxBuilder-Pro's 'Customize -> Splash Page' section).
(3) Make sure that you do not have any browser extensions active that change the user agent string (to simulate other browsers) and also make sure that your browser is not in Responsive Design Mode.

Edit:
I've just realised that you have posted in the Juicebox-Lite forum and the configuration options in bold above are supported by Juicebox-Pro only.
Juicebox-Lite uses the default values of screenMode="AUTO" and showSplashPage="AUTO" (these values cannot be changed in Juicebox-Lite) so just check #3 above.

This sounds like it might be a different problem.
However, if you can resolve your original problem, then this may no longer be an issue.

Unfortunately, your screenshot does not show enough information to help me to troubleshoot your problems.
Please post the URL to your gallery's web page so that I can see the problems for myself and investigate further.
Thank you.

Please check your gallery's web page for HTML errors with the W3C Markup Validation Service.
When a web page is rendered differently in different browsers, this can often be attributed to HTML errors on the page.
Different browsers may respond differently towards errors (and some may be more tolerant towards errors than others).
Run your web page's URL through the W3C Markup Validation Service and fix any errors found.
Once the code on your web page validates correctly, your web page should be rendered with greater predictability and consistency across different browsers.

I hope my notes above help.
However, if you continue to experience difficulties, please post back with the URL to your gallery's web page so that I can see the problems for myself and hopefully help further.
Once I am able to see your gallery live on your web server, I should hopefully be able to determine the cause of your problems and propose a solution.
Thank you.

You're welcome!

You're welcome. I hope you're able to sort out your gallery's web page.
If you continue to have problems, just let me know (and post a link to your gallery's web page) and I'll try to help further.

@Hurlas

With Juicebox-Pro, each gallery can have its own 'jbcore' folder and, therefore, its own password. (Please see the Password Protection support section for details.)
If you like, galleries can share a password, either by sharing a single 'jbcore' folder (see here for details) or by entering the same password into each gallery's 'pswd.php' file.

When using Showkase, all Juicebox-Pro galleries share the same 'jbcore' folder and, thus, all galleries use the same password.
This is just how Showkase works and it cannot be changed.

The first thing to note is that both of your web pages load the same gallery. (Both web pages are in the same directory and load the same embedding code.)
This might be your intention (to simply update the gallery on both pages) but I cannot be sure so I thought I should point this out in case it helps.

The 'config.xml' file for the gallery (displayed on both web pages) can be found here: https://www.soroptimistireland.com/config.xml
It contains only 6 <image> entries.

Maybe your FTP program is set to not replace existing files so when you upload the new 'config.xml' file (containing 16 images), the FTP program sees that there is already a 'config.xml' file on your web server and skips uploading the new version.
Make sure that your FTP program is set to overwrite existing files or delete the existing 'config.xml' file first, before uploading the new version in its place.

After uploading the new 'config.xml' file, clear your browser's cache and then view it directly in your browser (using the link above) to see what version it is.
If the file still shows 6 images instead of 16, then your web server may have some sort of server-side caching enabled.
Please check with your web host to see if they have server-side caching enabled on your hosting account and ask them how it can be disabled.

I hope my notes above point you in the right direction.

It seems very strange that you work fine with JuiceboxBuilder-Lite but not with JuiceboxBuilder-Pro. I expect that both applications share similar code with regard to image processing (with the exception that JuiceboxBuilder-Pro allows multiple image sizes and watermarks).

Are you using multiple image sizes or watermarks?
If so, try using only one image size (medium) and no watermark to see if this helps.

Have you tried using the exact same images in JuiceboxBuilder-Lite that cause JuiceboxBuilder-Pro to freeze? (You can install and run both JuiceboxBuilder-Lite and JuiceboxBuilder-Pro side by side on the same computer.)

Does JuiceboxBuilder-Pro freeze on the same image every time?
Perhaps you have a corrupt image within your batch that JuiceboxBuilder-Pro is choking on. (Even if an image opens in other programs, something as seemingly innocuous as corrupt metadata may prevent JuiceboxBuidler-Pro from processing the image.)

It might also be worth temporarily disabling any security software that you might have installed (at your own risk... please disconnect from the internet first) to see if this makes a difference. Avast's Ransomware Shield, for example, has been known to interfere with JuiceboxBuilder-Pro's functionality on a few occasions (although not with the symptoms that you describe). It's a long shot but a quick and easy thing to try and if it does not make a difference, then we can at least eliminate it as a possible cause.

Yes. The latest version is v1.5.1. (You can check the latest version on the Version History page.)

No. JuiceboxBuilder-Pro is a 32-bit application. (On a Windows 10 PC, JuiceboxBuilder is installed to the C:\Program Files (x86)\ folder.)

If you try to add many images to JuiceboxBuilder-Pro at once, then Adobe AIR (the platform on which JuiceboxBuilder-Pro runs) may not be able to allocate enough memory for the task at hand.
Even if your computer has plenty of free RAM, Adobe AIR applications are limited to around 1GB of memory allocation (as far as I am aware).
The workaround is usually to add your images in smaller batches.

This problem is usually encountered only when adding hundreds of images to a gallery at once.
I've never known this to happen when adding only 12 images.
Also, when this problem is encountered, JuiceboxBuilder-Pro is more likely to crash and close (rather than freeze whilst processing an image).

With this in mind, it looks like your problem might somehow be due to your source images.

Just in case it helps, how big are your source images (both in terms of resolution and file size)?
Also, what Mac OS are you using?

If possible, please zip and upload a few of your source images (and provide a download link) so that I can try to replicate your problem on my own PC.
(Please try to zip a complete batch of images that fails on your own Mac and let me know what image JuiceboxBuilder-Pro freezes on.)