The regressing bug (bug 1448286) removed a redundant call to
gBrowser.tabContainer.updateVisibility. It appears that removed call was
necessary for restoring the tabbar of windows that were originally opened as
dialogs.
In D53692, we tried to avoid the extra cost of removing and readding the tab if
we were restoring a single-tabbed window, but it turns out that it's required to
get around the above.
Differential Revision: https://phabricator.services.mozilla.com/D124358
c46f450d48
