Firefox 126+ implements CSS zoom in a way it affects width computed style
very slightly (`100.008px` instead of `100px`); accept that difference.
Add a test for support tests resolving the same under CSS zoom & without one.
That test uncovered Chrome failing the `reliableTrDimensions` support test
under zoom; the test has been fixed.
Fixes gh-5489
Closes gh-5495
Ref gh-5496
