"Query features" tool doesn't work

Recently "query features" started returning a black frame. Clearing cache/cookies doesn't help, appears in both FF 52 and Chrome 57; orange circle doesn't even disappear after click, looks like the request just hangs up.

pic

upd: XHR response header seems ok. But response text just has "Searching" fields which don't update over time.

<h2>
<a class="geolink" href="/"><span class="icon close"></span></a>
Query Features
</h2>

<div class="query-intro">
<p>Click on the map to find nearby features.</p>
</div>

<div id="query-nearby" class="query-results">
<h3>Nearby features</h3>
<img class="loader" src="/assets/searching-b66184be88a18bc2147e414ab67bde941db2507a69d455439a09d5280a8bdb63.gif" alt="Searching" />
<ul class="query-results-list"></ul>
</div>

<div id="query-isin" class="query-results">
<h3>Enclosing features</h3>
<img class="loader" src="/assets/searching-b66184be88a18bc2147e414ab67bde941db2507a69d455439a09d5280a8bdb63.gif" alt="Searching" />
<ul class="query-results-list"></ul>
</div>

upd: The tool works in Chrome Incognito window, but does not in Firefox Private mode.