missing sort menu, note vertical border to right of sort menu toggle

Browser tests sometimes fail on test2wiki, e.g.
https://integration.wikimedia.org/ci/view/BrowserTests/view/Echo+Flow/job/browsertests-Flow-test2.wikipedia.org-linux-firefox-sauce/280/testReport/junit/%28root%29/Sorting%20topics/Switch_topic_sorting_to_Recently_Active_Topics/

When I click Newest topics link
  And I click Recently active topics choice

timed out after 5 seconds, waiting for {:href=>/topiclist_sortby=updated/, :tag_name=>"a"} to become present (Watir::Wait::TimeoutError)

If you watch the movie (you'll laugh, you'll cry) or the screen shots, you see the "Newest topics v" menu toggle goes dark on hover/click[1] and a vertical border appears to its right, but its menu does not appear. I think this is a timing issue: you can reproduce by visiting a Flow board in a new private Firefox session and as soon as you see Newest topics, click it. Nothing appears except for the vertical border. When the menu fails to appear it will not appear on subsequent clicks, no matter how long you wait (until you reload the page).

The "Newest topics v" menu toggle should be invisible or disabled until its menu is functional. See also bug 72339 "Flow: sort menu broken in non-JavaScript".

[1] There's a UX inconsistency: mediawiki.ui buttons go _light_ on hover and only darken on click, this menu toggle that requires a click does not.

Version: master
Severity: normal

Attached: