Frontend Modals / Popups not working after 5.0 to 5.1 upgrade

Stackideas,

I just upgraded from 5.0.44 to 5.1.14 on a dev site.

Frontend welcome login works fine on this 5.1 dev site.

Our production site's modals and popup composer work fine in 5.0.44.

The 5.1 dev site's composer opens in a new tab (no longer a popup and I understand that's new to 5.1).
However, I'm unable to exit or close without composing using the Back button.
Also. all popups/modals like the Media manager or Post Cover are not working...nothing happens...acts like dead links.

I've tried with the Gecko engine on both Firefox and SeaMonkey, as well as the Chromium engine in Opera, all with popups enabled.

Joomla 3.8.1, PHP 5.6.31.

I'm using a Joomlashack template, JS_Novitas 1.1.1, with bootstrap's responsive behavior enabled. This is getting older now and

Our production site:
https://www.ppcitizensforlife.org

Our dev site:
https://www.ppcitizensforlife.org/new

Your prompt help will be appreciated either finding a missing setting (AJAX or Javascript?) or tracking down an issue with your new version and our template.

Regards,
Jim and John