> In that case, Blink and WebKit are changing to Firefox (and Edge)'s behavior The problem in FF isn't that they don't perform layout in the hidden iframe, it'

> In that case, Blink and WebKit are changing to Firefox (and Edge)'s behavior The problem in FF isn't that they don't perform layout in the hidden iframe, it's that `getComputedStyle` returns `null`, which happens to be a side effect of not performing layout in Gecko. If you read through the various related issues in your link I think you'll find that they are moving to standardize on not performing layout in hidden iframes, but `getComputedStyle` returning `null` is still a bug that Gecko intends to fix.