Index: test/synchronizer.js
===================================================================
--- a/test/synchronizer.js
+++ b/test/synchronizer.js
@@ -321,49 +321,49 @@
   {
     return [Cr.NS_OK, 200, "[Adblock]\n!Redirect: http://example.com/redirected\nbar"];
   });
 
   let requests;
 
   this.runScheduledTasks(30).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0], subscription, "Invalid redirect ignored");
+    test.equal([...FilterStorage.subscriptions()][0], subscription, "Invalid redirect ignored");
     test.equal(subscription.downloadStatus, "synchronize_connection_error", "Connection error recorded");
     test.equal(subscription.errors, 2, "Number of download errors");
 
     requests = [];
 
     this.registerHandler("/redirected", metadata =>
     {
       requests.push(this.getTimeOffset());
       return [Cr.NS_OK, 200, "[Adblock]\n! Expires: 8 hours\nbar"];
     });
 
     resetSubscription(subscription);
     return this.runScheduledTasks(15);
   }).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0].url, "http://example.com/redirected", "Redirect followed");
+    test.equal([...FilterStorage.subscriptions()][0].url, "http://example.com/redirected", "Redirect followed");
     test.deepEqual(requests, [0 + initialDelay, 8 + initialDelay], "Resulting requests");
 
     this.registerHandler("/redirected", metadata =>
     {
       return [Cr.NS_OK, 200, "[Adblock]\n!Redirect: http://example.com/subscription\nbar"];
     });
 
     subscription = Subscription.fromURL("http://example.com/subscription");
     resetSubscription(subscription);
-    FilterStorage.removeSubscription(FilterStorage.subscriptions[0]);
+    FilterStorage.removeSubscription([...FilterStorage.subscriptions()][0]);
     FilterStorage.addSubscription(subscription);
 
     return this.runScheduledTasks(2);
   }).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0], subscription, "Redirect not followed on redirect loop");
+    test.equal([...FilterStorage.subscriptions()][0], subscription, "Redirect not followed on redirect loop");
     test.equal(subscription.downloadStatus, "synchronize_connection_error", "Download status after redirect loop");
   }).catch(unexpectedError.bind(test)).then(() => test.done());
 };
 
 exports.testFallback = function(test)
 {
   Prefs.subscriptions_fallbackerrors = 3;
   Prefs.subscriptions_fallbackurl = "http://example.com/fallback?%SUBSCRIPTION%&%CHANNELSTATUS%&%RESPONSESTATUS%";
@@ -402,68 +402,68 @@
   {
     test.deepEqual(requests, [0 + initialDelay, 24 + initialDelay, 48 + initialDelay], "Stop trying if the fallback responds with Gone");
     test.equal(fallbackParams, "http://example.com/subscription&0&404", "Fallback arguments");
 
     // Fallback redirecting to a missing file
 
     subscription = Subscription.fromURL("http://example.com/subscription");
     resetSubscription(subscription);
-    FilterStorage.removeSubscription(FilterStorage.subscriptions[0]);
+    FilterStorage.removeSubscription([...FilterStorage.subscriptions()][0]);
     FilterStorage.addSubscription(subscription);
     requests = [];
 
     this.registerHandler("/fallback", metadata =>
     {
       return [Cr.NS_OK, 200, "301 http://example.com/redirected"];
     });
     return this.runScheduledTasks(100);
   }).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0].url, "http://example.com/subscription", "Ignore invalid redirect from fallback");
+    test.equal([...FilterStorage.subscriptions()][0].url, "http://example.com/subscription", "Ignore invalid redirect from fallback");
     test.deepEqual(requests, [0 + initialDelay, 24 + initialDelay, 48 + initialDelay, 72 + initialDelay, 96 + initialDelay], "Requests not affected by invalid redirect");
 
     // Fallback redirecting to an existing file
 
     resetSubscription(subscription);
     requests = [];
     redirectedRequests = [];
     this.registerHandler("/redirected", metadata =>
     {
       redirectedRequests.push(this.getTimeOffset());
       return [Cr.NS_OK, 200, "[Adblock]\n!Expires: 1day\nfoo\nbar"];
     });
 
     return this.runScheduledTasks(100);
   }).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0].url, "http://example.com/redirected", "Valid redirect from fallback is followed");
+    test.equal([...FilterStorage.subscriptions()][0].url, "http://example.com/redirected", "Valid redirect from fallback is followed");
     test.deepEqual(requests, [0 + initialDelay, 24 + initialDelay, 48 + initialDelay], "Stop polling original URL after a valid redirect from fallback");
     test.deepEqual(redirectedRequests, [48 + initialDelay, 72 + initialDelay, 96 + initialDelay], "Request new URL after a valid redirect from fallback");
 
     // Redirect loop
 
     this.registerHandler("/subscription", metadata =>
     {
       return [Cr.NS_OK, 200, "[Adblock]\n! Redirect: http://example.com/subscription2"];
     });
     this.registerHandler("/subscription2", metadata =>
     {
       return [Cr.NS_OK, 200, "[Adblock]\n! Redirect: http://example.com/subscription"];
     });
 
     subscription = Subscription.fromURL("http://example.com/subscription");
     resetSubscription(subscription);
-    FilterStorage.removeSubscription(FilterStorage.subscriptions[0]);
+    FilterStorage.removeSubscription([...FilterStorage.subscriptions()][0]);
     FilterStorage.addSubscription(subscription);
 
     return this.runScheduledTasks(100);
   }).then(() =>
   {
-    test.equal(FilterStorage.subscriptions[0].url, "http://example.com/redirected", "Fallback can still redirect even after a redirect loop");
+    test.equal([...FilterStorage.subscriptions()][0].url, "http://example.com/redirected", "Fallback can still redirect even after a redirect loop");
   }).catch(unexpectedError.bind(test)).then(() => test.done());
 };
 
 exports.testStateFields = function(test)
 {
   let subscription = Subscription.fromURL("http://example.com/subscription");
   FilterStorage.addSubscription(subscription);