Problems with Firefox (Jetpack carousel, share buttons, related pages/posts don't work)

Dear support

I realized that at some point my site has stopped functioning properly in Firefox. Brave (or Chrome based browsers) seem to work. Jetpack carousel, Ad to Any share buttons and related pages/posts don’t work). The share buttons are lost completely and the related articles/posts do not show up. I think even with Brave they do not come up in some articles. I have PHP 7.2 Sparkling 2.4.7 and Wordpress 5.7. I tried updating all of those, but with no help. Some issues even became worse. Like some Widget errors that are being discussed elsewhere on Wordpress support sites.

So I concluded it’s theme related. I also get error message at the themes page like this:

“Template is missing. Standalone themes need to have a index.php template file. Child themes need to have a Template header in the style.css stylesheet.”

When I originally created Child theme it worked as far as I can remember.

Can I link my site privately for you to check out?