Update:

Harman's link to AIR v33.1.1.385 has expired.

Until Haman publish a fixed version of AIR on their public download page, please use v33.1.1.502 from this page:
https://transfer.harman.com/message/yAj … vio19j765S

I have tested v33.1.1.502 myself and it works well (just like v33.1.1.385 did).

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

Will do!

This is certainly a problem but one which I cannot replicate myself.
I've just installed WP-Juicebox v1.5.1.3 under WordPress 5.7.2 and the 'Add Juicebox Gallery' button appears to the right side of the Gutenberg toolbar (next to the 'Preview' and 'Publish' buttons) as expected.
Are you using the built-in Gutenberg editor or the Classic editor a different custom editor?

Maybe you have a plugin which is somehow interfering with WP-Juicebox's functionality.
Try deactivating all your plugins (other than WP-Juicebox) and reactivate them, one-by-one, checking to see if  the 'Add Juicebox Gallery' button appears after each one to see if you can find a plugin which is conflicting with WP-Juicebox.

This is a sure sign that the update from Juicebox-Lite to Juicebox-Pro has not been successful. (The Juicebox logo does not appear in the lower right corner of any Pro galleries.)
Please try the Upgrading to Juicebox-Pro instructions again, making sure that you use the 'jbcore' folder from the Juicebox-Pro zip file and that you definitely overwrite the existing Lite 'jbcore' folder in the 'plugins/wp-juicebox' directory.

Please let me know how you get on.
Thanks!

It sounds like there's an underlying problem with Adobe AIR on your system.
As you are aware, clicking the 'Browse' button should open your system's native file chooser window.
I'm not sure what would prevent the file chooser window from displaying correctly but here are a few things to try:

Suggestion #1
If you have any third-party anti-virus or security software installed, then please try temporarily disabling it in case it is somehow interfering with JuiceboxBuilder-Pro's functionality.
(Please do so at your own risk and be sure to disconnect from the internet first.)

Suggestion #2
Clear all JuiceboxBuilder-Pro preferences and settings.
(1) Close JuiceboxBuilder-Pro
(2) Delete the following folders manually:

• /Users/Username/Library/Application Support/Adobe/AIR/ELS/JuiceboxBuilder-Pro

• /Users/Username/Library/Preferences/JuiceboxBuilder-Pro

(3) Run JuiceboxBuilder-Pro to see if this has resolved the problem.

Suggestion #3
Try uninstalling and then reinstalling Adobe AIR and make sure that you are using the latest version (v33.1.1.444).
You can download it from here: https://airsdk.harman.com/runtime
The problem sounds like an issue with Adobe AIR integrating with your operating system so hopefully a clean AIR installation will help.

Suggestion #4
Make sure that your operating system is up to date and that you have the most recent graphics drivers installed.

I hope that one of these suggestions helps you to resolve your problem.
Please let me know how you get on.
Thank you.

In a comment from a Harman GitHub Issues topic a couple of hours ago, A J W Frost (Harman staff) released a link to a web page containing Windows AIR runtime installers for v33.1.1.385 (the previous version) and v33.1.1.476 (a pre-release version).

You can now download v33.1.1.385 directly from Harman (without relying on software mirror sites).
I have experienced problems with the pre-release version (v33.1.1.476) so I would recommend using the last stable version (v33.1.1.385) for the time being.

Links:

Issues topic: https://github.com/airsdk/Adobe-Runtime … -833331811
AIR v33.1.1.385 temporary download page: https://transfer.harman.com/message/BYb … oGVLJ9CpSN
Harman AIR runtime download page (still offering v33.1.1.444): https://airsdk.harman.com/runtime

I appreciate the additional notes (and I'm glad that you have found a workflow that works for you) but I still don't fully understand your image ordering problem. (I guess I just don't know what order you'd like your images to be in. It sounds like you're looking for a non-algorithmically-sortable custom order.)
In JuiceboxBuilder, you can automatically order images by file name or by file date (using the 'Images -> Sort' option from the drop-down menu at the top). If neither of these two ordering structures is what you are looking for, then the only two options (to achieve a custom order) would be:
(1) drag and drop images into a custom order on the 'Images' tab.
(2) rename your images in the desired order so that the file name order works.
If you're looking for a custom order, then I don't think there's a third option and if what you are currently doing (#2) is faster than the alternative (#1), then stick with it!

Embedding a gallery generated by the Lightroom plugin is the same as embedding a gallery generated by JuiceboxBuilder.
The only difference is where you get the embedding code from.
In JuiceboxBuilder, you can copy the embedding code directly from the 'Publish' tab.
For the Lightroom plugin, open the gallery's index.html' file in a plain text editor and copy everything between the <!--START JUICEBOX EMBED--> and <!--END JUICEBOX EMBED--> tags.
Everything is the same thereafter.

With regard to the semi-colon, no problem. As you suggest, a stray semi-colon will not break anything (but if we knew where it was, we could perhaps tidy up the code).

In any case, I'm glad you've been able to work around your problems and that things are going well.
Your website looks great!

Sorry, when you said that you saw the "Config file not found." error in Safari, I thought that the problem might have been the local viewing issue noted in the forum thread I linked to.

On further investigation, it looks like the problem is with the use of double-quotes in some of your linkURLs (in your gallery's 'conffig.xml'; file), e.g.:

linkURL="Dunes II, oil on board, 32"H x 48"W"

The double-quote after '32' is closing off the linkURL's opening double-quote and the text after the double-quote is breaking the XML syntax.

7 thumbnails are displayed as the first error in the XML file appears in the data for the 8th image.

A linkURL is intended to be a URL (either relative or absolute) and the link is used when the visitor clicks the Open Image button or the Download Button. (If an image does not have a custom linkURL associated with it, then Juicebox will, by default, use the imageURL instead for the Open Image button and the Download button.)
Your linkURLs are not actually links (so your Download button will not work) and, even if your linkURLs were valid links, they should not really contain double-quotes. (Stick to web-safe alpha-numeric characters for URLs and all should be well.)

Just deselect the 'Link URL' checkbox (in the 'Image Info' control panel) and that should hopefully fix your problem.

(Thank you for providing all the files and information that you have. It has certainly made troubleshooting your problem that much easier. Initially, I opened your gallery's XML file in a text editor and missed the issue. It was not until I opened your gallery's XML file directly in a browser that I saw the problem.)

If you like, you can upgrade to the latest version (v1.5.1). Upgrades are free within the same major version number and download links always point towards the latest version (rather than the version you purchased).
Full instructions for upgrading can be found here.

Incidentally, I've removed the link to your 'juicebox.js' file. We don't want to make it easy for non-registered users to download Pro files (even though it's an old version and a single Pro file out of context will be of little use to anyone).
I appreciate you uploading so many files for troubleshooting, though. Thanks!

Update:

Unfortunately, there seems to be a problem with the latest version of the AIR runtime for Windows (v33.1.1.444).
A clean install appears to be successful but does not allow any AIR applications to be installed (and AIR itself cannot be uninstalled via the Control Panel).
Likewise, an upgrade from a previous version of AIR appears to be successful but not all files are overwritten, resulting in similar problems.

I reported the problem to Harman earlier today and they have confirmed that there is a problem with the current Windows installer.
For reference, here is my report to Harman: https://github.com/Gamua/Adobe-Runtime- … ssions/788

Hopefully they will be able to fix the problem soon but, in the meantime, a suitable workaround is as follows:

(1) Uninstall Adobe AIR. If you cannot uninstall Adobe AIR via the Control Panel, then delete the following folder manually:

• C:\Program Files (x86)\Common Files\Adobe AIR

(2) Download and install the previous version of AIR (v33.1.1.385).
Harman do not make previous versions available for download but you can still download it from here: https://www.filecroco.com/download-adobe-air/.
The file from filecroco.com is the official Harman release of AIR v33.1.1.385 (genuine, clean and safe to use).
I found the SHA256 hash for the 'AdobeAIR.exe' v33.1.1.385 file on a Harman web page archived by archive.org (search for "https://airsdk.harman.com/runtime" and select the page dated 26 January 2021) and it matches the SHA256 hash of the file from filecroco.com.

Sorry for the inconvenience but this should work fine until Harman releases a new AIR runtime for Windows.

I've glad you've got JuiceboxBuilder-Pro up and running.
Thanks for letting me know.

That's great! Thank you for letting me know.
Any chance you could let me know what fixed the problem? It might help if other users report a similar problem. Thanks!

Thank you for the update.
I'm sorry to hear that you are still having problems.

That's normal and expected. When using the new Harman AIR runtime, you'll see the Harman splash page when running any AIR application.

Something must have happened for this problem to have occurred and if you don't remember doing anything yourself, then perhaps some other background update has somehow caused the problem.
Perhaps you could use System Restore and restore your system to a point in time before the problem first happened.

Otherwise, knowing that you've already uninstalled and reinstalled Adobe AIR, I'd now recommend a full uninstall/reinstall of JuiceboxBuilder-Pro (and JuiceboxBuilder-Lite).
Check out the procedure listed as #11 in this forum post.
Be sure to manually delete the folders listed between uninstalling and reinstalling.
This is very important. If there is corrupt data in the ELS folder, then deleting it may help to resolve the problem.

When following the procedure for JuiceboxBuilder-Lite, just replace all instances of 'JuiceboxBuilder-Pro' in the instructions with 'JuiceboxBuilder-Lite'.

Quick update...

The file from filecroco.com checks out OK. It's clean and safe to use.
I found the SHA256 hash for the 'AdobeAIR.exe' v33.1.1.385 file on Harman's old web page archived by archive.org (search for "https://airsdk.harman.com/runtime" and select the page dated 26 January 2021) and it matches the SHA256 hash of the file from filecroco.com.

(It's always best to check the hash after downloading, though, just in case the file on the server changes.)