Forms not displaying using shortcode on Firefox desktop

I am using a simple shortcode in a text widget in the footer [activecampaign form=1] under SUBSCRIBE TO OUR MAILING LIST. For some reason the form is not displaying at all on Firefox desktop on Mac (I tested on two different Macs). It displays properly on Safari and Chrome on Mac and also in various browsers in iOS. Ironically it displays properly on Firefox when using a localhost version of the site on desktop.

This problem may have started after updating to WP 5.5 but I am not sure of this.

Any suggestions? Thank you!

The page I need help with: [log in to see the link]