--- a/devtools/client/aboutdebugging/test/browser_service_workers.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers.js
@@ -8,17 +8,17 @@
 const SERVICE_WORKER = URL_ROOT + "service-workers/empty-sw.js";
 const TAB_URL = URL_ROOT + "service-workers/empty-sw.html";
 
 add_task(function* () {
   yield enableServiceWorkerDebugging();
 
   let { tab, document } = yield openAboutDebugging("workers");
 
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   let serviceWorkersElement = getServiceWorkerList(document);
 
   yield waitUntil(() => {
     // Check that the service worker appears in the UI
     let names = [...document.querySelectorAll("#service-workers .target-name")];
     names = names.map(element => element.textContent);
     return names.includes(SERVICE_WORKER);

--- a/devtools/client/aboutdebugging/test/browser_service_workers_fetch_flag.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_fetch_flag.js
@@ -7,17 +7,17 @@
 // but http:// is ok with dom.serviceWorkers.testing.enabled turned on.
 const EMPTY_SW_TAB_URL = URL_ROOT + "service-workers/empty-sw.html";
 const FETCH_SW_TAB_URL = URL_ROOT + "service-workers/fetch-sw.html";
 
 function* testBody(url, expecting) {
   yield enableServiceWorkerDebugging();
   let { tab, document } = yield openAboutDebugging("workers");
 
-  let swTab = yield addTab(url);
+  let swTab = yield addTab(url, {background: true});
 
   let serviceWorkersElement = getServiceWorkerList(document);
 
   info("Wait for fetch flag.");
   yield waitUntil(() => {
     let fetchFlags =
       [...document.querySelectorAll("#service-workers .service-worker-fetch-flag")];
     fetchFlags = fetchFlags.map(element => element.textContent);

--- a/devtools/client/aboutdebugging/test/browser_service_workers_push.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_push.js
@@ -17,17 +17,17 @@ const TAB_URL = URL_ROOT + "service-work
 add_task(function* () {
   yield enableServiceWorkerDebugging();
   let { tab, document } = yield openAboutDebugging("workers");
 
   // Listen for mutations in the service-workers list.
   let serviceWorkersElement = getServiceWorkerList(document);
 
   // Open a tab that registers a push service worker.
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   info("Make the test page notify us when the service worker sends a message.");
 
   yield ContentTask.spawn(swTab.linkedBrowser, {}, function () {
     let win = content.wrappedJSObject;
     win.navigator.serviceWorker.addEventListener("message", function (event) {
       sendAsyncMessage(event.data);
     });

--- a/devtools/client/aboutdebugging/test/browser_service_workers_push_service.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_push_service.js
@@ -53,17 +53,17 @@ add_task(function* () {
   };
 
   let { tab, document } = yield openAboutDebugging("workers");
 
   // Listen for mutations in the service-workers list.
   let serviceWorkersElement = document.getElementById("service-workers");
 
   // Open a tab that registers a push service worker.
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   info("Wait until the service worker appears in about:debugging");
   yield waitUntilServiceWorkerContainer(SERVICE_WORKER, document);
 
   yield waitForServiceWorkerActivation(SERVICE_WORKER, document);
 
   // Wait for the service worker details to update.
   let names = [...document.querySelectorAll("#service-workers .target-name")];

--- a/devtools/client/aboutdebugging/test/browser_service_workers_start.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_start.js
@@ -20,17 +20,17 @@ add_task(function* () {
   yield pushPref("dom.serviceWorkers.idle_extended_timeout", SW_TIMEOUT);
 
   let { tab, document } = yield openAboutDebugging("workers");
 
   // Listen for mutations in the service-workers list.
   let serviceWorkersElement = getServiceWorkerList(document);
 
   // Open a tab that registers an empty service worker.
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   // Wait for the service-workers list to update.
   info("Wait until the service worker appears in about:debugging");
   yield waitUntilServiceWorkerContainer(SERVICE_WORKER, document);
 
   info("Ensure that the registration resolved before trying to interact with " +
     "the service worker.");
   yield waitForServiceWorkerRegistered(swTab);

--- a/devtools/client/aboutdebugging/test/browser_service_workers_status.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_status.js
@@ -16,17 +16,17 @@ add_task(function* () {
   yield pushPref("dom.serviceWorkers.idle_timeout", SW_TIMEOUT);
   yield pushPref("dom.serviceWorkers.idle_extended_timeout", SW_TIMEOUT);
 
   let { tab, document } = yield openAboutDebugging("workers");
 
   // Listen for mutations in the service-workers list.
   let serviceWorkersElement = getServiceWorkerList(document);
 
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   info("Wait until the service worker appears in about:debugging");
   let container = yield waitUntilServiceWorkerContainer(SERVICE_WORKER, document);
 
   // We should ideally check that the service worker registration goes through the
   // "registering" and "running" steps, but it is difficult to workaround race conditions
   // for a test running on a wide variety of platforms. Due to intermittent failures, we
   // simply check that the registration transitions to "stopped".

--- a/devtools/client/aboutdebugging/test/browser_service_workers_timeout.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_timeout.js
@@ -15,17 +15,17 @@ add_task(function* () {
   yield enableServiceWorkerDebugging();
   yield pushPref("dom.serviceWorkers.idle_timeout", SW_TIMEOUT);
   yield pushPref("dom.serviceWorkers.idle_extended_timeout", SW_TIMEOUT);
 
   let { tab, document } = yield openAboutDebugging("workers");
 
   let serviceWorkersElement = getServiceWorkerList(document);
 
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   info("Wait until the service worker appears in about:debugging");
   yield waitUntilServiceWorkerContainer(SERVICE_WORKER, document);
 
   // Ensure that the registration resolved before trying to connect to the sw
   yield waitForServiceWorkerRegistered(swTab);
   ok(true, "Service worker registration resolved");
 

--- a/devtools/client/aboutdebugging/test/browser_service_workers_unregister.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_unregister.js
@@ -15,17 +15,17 @@ const SERVICE_WORKER = SCOPE + "empty-sw
 const TAB_URL = SCOPE + "empty-sw.html";
 
 add_task(function* () {
   yield enableServiceWorkerDebugging();
 
   let { tab, document } = yield openAboutDebugging("workers");
 
   // Open a tab that registers an empty service worker.
-  let swTab = yield addTab(TAB_URL);
+  let swTab = yield addTab(TAB_URL, { background: true });
 
   info("Wait until the service worker appears in about:debugging");
   yield waitUntilServiceWorkerContainer(SERVICE_WORKER, document);
 
   yield waitForServiceWorkerActivation(SERVICE_WORKER, document);
 
   info("Ensure that the registration resolved before trying to interact with " +
     "the service worker.");