I can't believe anyone would seriously think a particular distro is the way to go for getting AMD video working. The distro doesn't matter.
After a few hours googling and experimenting, I have added 'amd_iommu=on iommu=pt' to the kernel boot line and have not seen the issue. The 'amd_iommu=on'...
I'm having the SAME problem... which is how I found your post. This issue is not just occurring in Firefox for me. Also seeing this in other programs. I did perform the BIOS upgrade to the latest version and this did not solve the problem.