Plugin is trying to load fonts and icons over http on an https site

Hello!

Trying to track down an issue with Hustle plugin. It appears that the theme itself may be having a problem. This only occurs now in Firefox, as we have installed the SSL Secure Content Fixer installed. These are some of the errors we see in the Developer Tools console:

10:46:37.405 Blocked loading mixed active content “https://mufonsymposium.com/wp-content/plugins/wordpress-popup/assets/hustle-ui/fonts/hustle-icons-font.woff”

css-logic.js:520:31

10:46:37.426 Blocked loading mixed active content “https://mufonsymposium.com/wp-content/plugins/wordpress-popup/assets/hustle-ui/fonts/hustle-icons-font.woff2”

ufo-in-art

10:46:37.429 downloadable font: failed to start download (font-family: “hustle-icons-font” style:normal weight:400 stretch:100 src index:1): content blocked source: https://mufonsymposium.com/wp-content/plugins/wordpress-popup/assets/hustle-ui/fonts/hustle-icons-font.woff2

10:46:37.429 Blocked loading mixed active content “https://mufonsymposium.com/wp-content/plugins/wordpress-popup/assets/hustle-ui/fonts/hustle-icons-font.woff”

ufo-in-art

10:46:37.429 downloadable font: failed to start download (font-family: “hustle-icons-font” style:normal weight:400 stretch:100 src index:2): content blocked source:?https://mufonsymposium.com/wp-content/plugins/wordpress-popup/assets/hustle-ui/fonts/hustle-icons-font.woff

There are other plugins with the same issue, and all their support staff are telling me that the theme is somehow to be at fault? What files or database tables should I be looking at to find out where the https:// references are coming from?

Thank you!

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