[Session Bookmarks] [e10s] Doesn't work correctly with enabled Electrolysis (multi-process mode)

[Infocatcher]

Throws here:

            let isPrivate = "PrivateBrowsingUtils" in window
                && PrivateBrowsingUtils.isWindowPrivate(tab.linkedBrowser.contentWindow) // <---
                || tab.hasAttribute(privateAttr);

Also not only here because remote frame not yet initialized.