I don't know if all these the-iframe-element WPT failures have the same cause, but it seems likely. If you would rather I file separate bugs for each test case, just let me know.

https://searchfox.org/mozilla-central/source/testing/web-platform/meta/html/semantics/embedded-content/the-iframe-element/iframe-modify-scrolling-attr-to-yes.html.ini

if fission: ERROR

https://searchfox.org/mozilla-central/source/testing/web-platform/meta/html/semantics/embedded-content/the-iframe-element/iframe-with-base.html.ini

if fission: ERROR

https://searchfox.org/mozilla-central/source/testing/web-platform/meta/html/semantics/embedded-content/the-img-element/adopt-from-image-document.html.ini

if fission: ERROR

The DOM Fission team is relying on feature teams to debug and fix Fission failures in their tests. If the failure looks like a bug in Fission's DOM or IPC changes, you can send the bug back to me.

We're hoping to enable Fission for a subset of Nightly users in early Q3, so we would like WPT tests to be green for Fission by end of Q2. Whether a particular test failure actually blocks shipping Fission is up to the discretion of the feature team. You all would know better than the DOM Fission which test failures are most important.

You can enable Fission when running WPT tests locally using mach wpt --enable-fission.

Hi John, please take a look, investigate and suggest the importance/priority of these. Thank you.

Yes, I'll take a look. Keep NI for tracking.

The three tests only happened when --enable-fission and have the same error which is UnknownError: SecurityError: Permission denied to access property "windowUtils" on cross-origin object.

flushWindow@chrome://marionette/content/listener.js:1715:17
flushWindow@chrome://marionette/content/listener.js:1733:18
flushRendering@chrome://marionette/content/listener.js:1736:14
maybeResolve@chrome://marionette/content/listener.js:1809:7
paintComplete/<@chrome://marionette/content/listener.js:1824:5
paintComplete@chrome://marionette/content/listener.js:1807:10
reftestWait@chrome://marionette/content/listener.js:1765:9
async*dispatch/</req<@chrome://marionette/content/listener.js:525:17
dispatch/<@chrome://marionette/content/listener.js:520:15
MessageListener.receiveMessage*startListeners@chrome://marionette/content/listener.js:605:21
registerSelf@chrome://marionette/content/listener.js:501:5
@chrome://marionette/content/listener.js:1855:1

(In reply to John Dai[:jdai] from comment #4)

The three tests only happened when --enable-fission and have the same error which is UnknownError: SecurityError: Permission denied to access property "windowUtils" on cross-origin object.

I think that SecurityError is Marionette test runner bug 1574508. No need for you to spend any more time debugging this test until bug 1574508 is fixed.

Tracking WPT Fission bugs for Fission M6b (Q2)

Fixed by bug 1635904.