If backdrop-filter is used on an element inside an iframe, the iframe's background is transparent in the filtered backdrop computation. The background of an iframe is technically transparent, but should maybe be white when computing a filtered backdrop.

The spec isn't exactly clear on this and Chrome gives the iframe a white background when processing this effect, Markus do you know if we are doing the correct thing here or if Chrome is correct?

See https://codepen.io/andreasstorm/pen/jqLGdQ

Hmm, I don't think Chrome actually pulls the white background into the iframe. I rather think that it doesn't consider iframes as BackdropRoot boundaries and instead establishes the backdrop root in the parent document around the <iframe> element and its white background color.

And yes, I agree it would be good to get this ambiguity clarified in the spec.

This has become better. It's almost fixed.
Remaining problem: Picture caching tiles become smaller and the lower ones are not instantly updated when they should be.

bug 1606328 is about the remaining problem.

Although comment 1 doesn't seem to be reproducible, duplicates are still reproducible.

(In reply to Darkspirit from comment #7)

Although comment 1 doesn't seem to be reproducible, duplicates are still reproducible.

bug 1613506: https://codepen.io/chaofix/pen/003d4fc45a1c892f96719de6dee5c975 is not getting enough blur

The testcase in comment 1, comment 8 and bug 1578703 seem to be fixed. The testcase in comment 1 has a strange interaction with overlay scrollbars (unrelated to iframes) which I've spun into bug 1769953