[e10s] Unable to restore closed private tabs

[Infocatcher]

Disabled by default, for extensions.privateTab.rememberClosedPrivateTabs = true

[from Firefox 52.0a2 (2017-01-10)]
resource:///modules/sessionstore/SessionStore.jsm
SessionStoreInternal.undoCloseTab()
-> SessionStoreInternal.restoreTab()

    if ("attributes" in tabData) {
      // Ensure that we persist tab attributes restored from previous sessions.
      Object.keys(tabData.attributes).forEach(a => TabAttributes.persist(a));
    }
    ...
    browser.messageManager.sendAsyncMessage("SessionStore:restoreHistory",
                                            {tabData: tabData, epoch: epoch, loadArguments});

chrome://browser/content/content-sessionStore.js
--> MessageListener.receiveMessage()
-> MessageListener.restoreHistory()
-> sendSyncMessage("SessionStore:restoreHistoryComplete", …)

resource:///modules/sessionstore/SessionStore.jsm
--> SessionStoreInternal.receiveMessage()

        let event = win.document.createEvent("Events");
        event.initEvent("SSTabRestoring", true, false);
        tab.dispatchEvent(event);

So, loading will be started before "SSTabRestoring" and in non-private mode.

[Infocatcher]

Looks like we can receive "SessionStore:restoreHistory" in our frame script and check for

message.data.tabData.attributes["privateTab-isPrivate"]