It looks like there is an error in number handling. FAIL new MouseEvent('eventType', { clientX: 2147483647 }).clientX should be 2147483647. Was -1. FAIL new MouseEvent('eventType', { clientX: -2147483648 }).clientX should be -2147483648. Was 0. FAIL new MouseEvent('eventType', { clientY: 2147483647 }).clientY should be 2147483647. Was -1. FAIL new MouseEvent('eventType', { clientY: -2147483648 }).clientY should be -2147483648. Was 0.
We don't have any platform specific expectation for following test while searching on 'searchfox.org' (wubkat) and it seems to have been resolved long time back and currently seems to be non-issue. Marking this as 'RESOLVED CONFIGURATION CHANGED'.