Today for the first time I had a sudden "crash while just browsing with
Firefox" while using the amggpu.vm_update_mode=3 parameter with the
current-as-of-today amd-staging-drm-next
(bb2e406ba66c2573b68e609e148cab57b1447095) with patch 
https://bugs.freedesktop.org/attachment.cgi?id=140418 applied on top.

Different kernel messages than with previous crashed of this kind were emitted:

Jul 07 01:08:20 ryzen kernel: amdgpu 0000:0a:00.0: GPU fault detected: 146
0x0c80440c
Jul 07 01:08:20 ryzen kernel: amdgpu 0000:0a:00.0:  
VM_CONTEXT1_PROTECTION_FAULT_ADDR   0x00100190
Jul 07 01:08:20 ryzen kernel: amdgpu 0000:0a:00.0:  
VM_CONTEXT1_PROTECTION_FAULT_STATUS 0x0E04400C
Jul 07 01:08:20 ryzen kernel: amdgpu 0000:0a:00.0: VM fault (0x0c, vmid 7,
pasid 32768) at page 1048976, read from 'TC1' (0x54433100) (68)
Jul 07 01:08:25 ryzen kernel: [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring
gfx timeout, last signaled seq=75244, last emitted seq=75245
Jul 07 01:08:25 ryzen kernel: amdgpu 0000:0a:00.0: GPU reset begin!

Hope this helps somehow.