I am running Windows 10, FFCore 6.0.2 and the Firefox browser. I do not see the issue. One idea -- Did you try performing a user sign out?
In the FF Core region settings I set "mm" as measurement units.
In my system locale "metric" is set as measurement system.
FF Core ignores all that and uses inches everywhere instead.
1) How is this even possible?
2) How to fix this?
Tested this in Firefox and MS Edge, no difference, relaunching browsers does nothing.
This is on Winows 10.
Tested on another machine running Windows 7 in MS Edge - same system locale settings, but there it works fine, with "mm" used as measurement units.
* update - I spoke too soon, after a few page refreshes second machine is also displaying inches now...