--- a/devtools/client/netmonitor/src/netmonitor-controller.js
+++ b/devtools/client/netmonitor/src/netmonitor-controller.js
@@ -542,17 +542,17 @@ NetworkEventsHandler.prototype = {
 
   pushPayloadToQueue(id, payload) {
     let queuedPayload = this.getPayloadFromQueue(id);
 
     if (!queuedPayload) {
       queuedPayload = { id, payload };
     } else {
       // Merge upcoming networkEventUpdate payload into existing one
-      queuedPayload = { id, payload: Object.assign({}, queuedPayload, payload) };
+      queuedPayload = { id, payload: Object.assign(queuedPayload, payload) };
     }
 
     this.payloadQueue.push(queuedPayload);
   },
 
   async updateRequest(id, data) {
     let {
       mimeType,

--- a/devtools/client/netmonitor/test/browser_net_security-tab-visibility.js
+++ b/devtools/client/netmonitor/test/browser_net_security-tab-visibility.js
@@ -63,16 +63,17 @@ add_task(function* () {
        "Security state has not yet arrived.");
     is(!!document.querySelector("#security-tab"), testcase.visibleOnNewEvent,
       "Security tab is " + (testcase.visibleOnNewEvent ? "visible" : "hidden") +
       " after new request was added to the menu.");
 
     info("Waiting for security information to arrive.");
     yield onSecurityInfo;
 
+    yield waitUntil(() => !!getSelectedRequest(gStore.getState()).securityState);
     ok(getSelectedRequest(gStore.getState()).securityState,
        "Security state arrived.");
     is(!!document.querySelector("#security-tab"), testcase.visibleOnSecurityInfo,
        "Security tab is " + (testcase.visibleOnSecurityInfo ? "visible" : "hidden") +
        " after security information arrived.");
 
     info("Waiting for request to complete.");
     yield onComplete;

--- a/devtools/client/netmonitor/test/browser_net_simple-request-data.js
+++ b/devtools/client/netmonitor/test/browser_net_simple-request-data.js
@@ -86,18 +86,24 @@ function test() {
         document,
         getDisplayedRequests(gStore.getState()),
         requestItem,
         "GET",
         SIMPLE_SJS
       );
     });
 
-    monitor.panelWin.once(EVENTS.RECEIVED_REQUEST_HEADERS, () => {
+    monitor.panelWin.once(EVENTS.RECEIVED_REQUEST_HEADERS, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.requestHeaders;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
+
       ok(requestItem.requestHeaders,
         "There should be a requestHeaders data available.");
       is(requestItem.requestHeaders.headers.length, 10,
         "The requestHeaders data has an incorrect |headers| property.");
       isnot(requestItem.requestHeaders.headersSize, 0,
         "The requestHeaders data has an incorrect |headersSize| property.");
       // Can't test for the exact request headers size because the value may
       // vary across platforms ("User-Agent" header differs).
@@ -106,17 +112,22 @@ function test() {
         document,
         getDisplayedRequests(gStore.getState()),
         requestItem,
         "GET",
         SIMPLE_SJS
       );
     });
 
-    monitor.panelWin.once(EVENTS.RECEIVED_REQUEST_COOKIES, () => {
+    monitor.panelWin.once(EVENTS.RECEIVED_REQUEST_COOKIES, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.requestCookies;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       ok(requestItem.requestCookies,
         "There should be a requestCookies data available.");
       is(requestItem.requestCookies.cookies.length, 2,
         "The requestCookies data has an incorrect |cookies| property.");
 
       verifyRequestItemTarget(
@@ -127,17 +138,22 @@ function test() {
         SIMPLE_SJS
       );
     });
 
     monitor.panelWin.once(EVENTS.RECEIVED_REQUEST_POST_DATA, () => {
       ok(false, "Trap listener: this request doesn't have any post data.");
     });
 
-    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_HEADERS, () => {
+    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_HEADERS, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.responseHeaders;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       ok(requestItem.responseHeaders,
         "There should be a responseHeaders data available.");
       is(requestItem.responseHeaders.headers.length, 10,
         "The responseHeaders data has an incorrect |headers| property.");
       is(requestItem.responseHeaders.headersSize, 330,
         "The responseHeaders data has an incorrect |headersSize| property.");
@@ -146,34 +162,47 @@ function test() {
         document,
         getDisplayedRequests(gStore.getState()),
         requestItem,
         "GET",
         SIMPLE_SJS
       );
     });
 
-    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_COOKIES, () => {
+    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_COOKIES, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.responseCookies;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       ok(requestItem.responseCookies,
         "There should be a responseCookies data available.");
       is(requestItem.responseCookies.cookies.length, 2,
         "The responseCookies data has an incorrect |cookies| property.");
 
       verifyRequestItemTarget(
         document,
         getDisplayedRequests(gStore.getState()),
         requestItem,
         "GET",
         SIMPLE_SJS
       );
     });
 
-    monitor.panelWin.once(EVENTS.STARTED_RECEIVING_RESPONSE, () => {
+    monitor.panelWin.once(EVENTS.STARTED_RECEIVING_RESPONSE, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.httpVersion &&
+               requestItem.status &&
+               requestItem.statusText &&
+               requestItem.headersSize;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       is(requestItem.httpVersion, "HTTP/1.1",
         "The httpVersion data has an incorrect value.");
       is(requestItem.status, "200",
         "The status data has an incorrect value.");
       is(requestItem.statusText, "Och Aye",
         "The statusText data has an incorrect value.");
@@ -188,17 +217,25 @@ function test() {
         SIMPLE_SJS,
         {
           status: "200",
           statusText: "Och Aye"
         }
       );
     });
 
-    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_CONTENT, () => {
+    monitor.panelWin.once(EVENTS.RECEIVED_RESPONSE_CONTENT, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.transferredSize &&
+               requestItem.contentSize &&
+               requestItem.mimeType &&
+               requestItem.responseContent;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       is(requestItem.transferredSize, "12",
         "The transferredSize data has an incorrect value.");
       is(requestItem.contentSize, "12",
         "The contentSize data has an incorrect value.");
       is(requestItem.mimeType, "text/plain; charset=utf-8",
         "The mimeType data has an incorrect value.");
@@ -228,17 +265,22 @@ function test() {
           type: "plain",
           fullMimeType: "text/plain; charset=utf-8",
           transferred: L10N.getFormatStrWithNumbers("networkMenu.sizeB", 12),
           size: L10N.getFormatStrWithNumbers("networkMenu.sizeB", 12),
         }
       );
     });
 
-    monitor.panelWin.once(EVENTS.UPDATING_EVENT_TIMINGS, () => {
+    monitor.panelWin.once(EVENTS.UPDATING_EVENT_TIMINGS, async () => {
+      await waitUntil(() => {
+        let requestItem = getSortedRequests(gStore.getState()).get(0);
+        return requestItem.eventTimings;
+      });
+
       let requestItem = getSortedRequests(gStore.getState()).get(0);
 
       is(typeof requestItem.totalTime, "number",
         "The attached totalTime is incorrect.");
       ok(requestItem.totalTime >= 0,
         "The attached totalTime should be positive.");
 
       verifyRequestItemTarget(