Hello,
I have tested your site in Firefox browser and your site footer is shown alright. But when I tried ctrl+F5 as you said to refresh the page footer content is there but it is invisible in the firefox browser.
Screenshot before refreshing: https://jmp.sh/J54eMAj
Screenshot after refresh the page: https://jmp.sh/djnej3y
Please deactivate all the plugins not related to the theme and switch the parent theme, check the issue, if the problem remains, leave the plugins not activated and provide the site admin access to the private area.
Best Regards