Merge pull request #1850 from mozilla/issue_1849_round_timestamp_down

Round the server timestamp DOWN to the nearest 10 minutes.

resources/static/shared/modules/interaction_data.js

@@ -124,9 +124,9 @@ BrowserID.Modules.InteractionData = (function() {
 
     // server_time is sent in milliseconds. The promise to users and data
     // safety is the timestamp would be at a 10 minute resolution.  Round to the
-    // nearest 10 minute mark.
+    // previous 10 minute mark.
     var TEN_MINS_IN_MS = 10 * 60 * 1000,
-        roundedServerTime = Math.round(result.server_time / TEN_MINS_IN_MS) * TEN_MINS_IN_MS;
+        roundedServerTime = Math.floor(result.server_time / TEN_MINS_IN_MS) * TEN_MINS_IN_MS;
 
     var currentData = {
       event_stream: self.initialEventStream,