Not sure if relevant, but: Mentioning bug 1797558 comment 34 as a possible source of investigation **especially** since this behavior seems intermittent. Over in bug 1891008 in this [patch](https://phabricator.services.mozilla.com/D207314#7119802) , WPT needed to adjust the window opener from geckoview-window-created to browser-delayed-startup-finished to fix intermittent timeouts. Which, was originally imitated web extensions window opener.
Bug 1861685 Comment 8 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
Not sure if relevant, but: Mentioning bug 1797558 comment 34 as a possible source of investigation **especially** since this behavior seems intermittent. Over in bug 1891008 in this [patch](https://phabricator.services.mozilla.com/D207314#7119802) , WPT needed to adjust the window opener from geckoview-window-created to browser-delayed-startup-finished to fix intermittent timeouts. Which, was originally imitating the web extensions window opener.