Hi, PYUREcrew!
Until now we didn’t have such a problem with the theme.
I checked your allegations on our site and I can confirm that everything works normally on the Firefox browser.
What version of Firefox do you use? (update if necessary).
Have you tried to temporarily turn off all active plugins? If not, do it and check again. If the customizer is working, try to turn on the plugins one at a time, until the problem reoccurs again. This way you will determine which plugin (s) is the problem (if any).
If after that, the problem persists, please give me your WP login credentials so I can check the problem directly on your site.