Hi Tenebreaux 👋 Welcome back to the community forum! Thanks for posting.
Sorry to hear you have been having some difficulties paying via My VM on Firefox! As Newapollo has already advised, there shouldn't be any issue using any browser with the site - there are not any known issues we are aware of.
Have you tried clearing the cookies and cache on your browser? Or using a 'private' version of the browser to see if this works?
You can also try using an alternative device (this will help determine if the issue is isolated to your browser)
You can also pay via the My VM app 👉 https://virg.in/myvmapp or any of the other methods listed here 👉 https://www.virginmedia.com/help/billing-and-payment/make-a-payment
Hope this helps! Let us know how you get on with the troubleshooting, and if you need further support. Thanks for your patience in the meantime! 🌞