The original HTML/CSS specifications were unclear about the intended behavior for elements inside display:none iframes. [Do they get CSS boxes? Are they rendered?] This has led to a divergence in behavior between UAs. The specs are in the process of being clarified, and the new spec matches the behavior of Edge and Gecko [which do not perform box construction or layout]. Note that Chrome's current behavior has negative performance implications. https://github.com/whatwg/html/issues/1813