It is Safari. The example one is a MacBook Air 2019 running Mojave 10.14.16 although several others on different Macs report what I also saw on Browser Stack - you try to place the cursor in the box but it won't stay in the box. If you click the magnifying glass, you get all products as a result as if you did a blank search. Hope that's enough of a clue. As an extra point, the Search does work with Chrome on the same MAC so it does seem browser-related.