Intermittent FAIL on /_mozilla/css/inline_block_margin_auto_zero_a.html

[ferjm]

{"status": "FAIL", "group": "default", "message": "/_mozilla/css/inline_block_margin_auto_zero_a.html 4e6ec2a4e7504e5c4bb739eb4fad793251d3180f\n/_mozilla/css/inline_block_margin_auto_zero_ref.html 151016448c96f116b27a512f03fc6c39c50e29ee\nTesting 4e6ec2a4e7504e5c4bb739eb4fad793251d3180f == 151016448c96f116b27a512f03fc6c39c50e29ee", "stack": null, "subtest": null, "test": "/_mozilla/css/inline_block_margin_auto_zero_a.html", "line": 30788, "action": "test_result", "expected": "PASS"}