Visual artifacts in Firefox after bus_space changes

[David Brownlee <abs%absd.org@localhost>]

I'm seeing visual artifacts in Firefox - I believe after
http://releng.netbsd.org/cgi-bin/req-9.cgi?show=566 was pulled up to
netbsd-9, and from a quick test with a current kernel

its as if a partial screen update can happen, when drawing a new
character when typing (eg into gmail or slack), highlighting some text
or even updating a screen element on hover. Its quickly replaced with
the correct content.

Its sometimes quite subtle, and occasionally very unsubtle.

Two quick videos indicating the issue

https://photos.google.com/share/AF1QipNaEbA8nrfrK1EpGqvOVjt_hLMtThJQTV_z7XWqlOExJGHsaktPi8V9qxEOW0zi5Q?key=VkV1YkVabHh3TVFwLUJsQTlGMUIxWWNBSndUb01R

This is on a Thinkpad T480
i915drmkms0 at pci0 dev 2 function 0: Intel UHD Graphics 620 (GT2) (rev. 0x07)
intel(0): Using Kernel Mode Setting driver: i915, version 1.6.0 20151010

Is anyone else seeing similar?

Thanks

David