--- a/dom/push/test/xpcshell/head-http2.js
+++ b/dom/push/test/xpcshell/head-http2.js
@@ -1,8 +1,19 @@
+// Returns the test H/2 server port, throwing if it's missing or invalid.
+function getTestServerPort() {
+  let portEnv = Cc["@mozilla.org/process/environment;1"]
+                  .getService(Ci.nsIEnvironment).get("MOZHTTP2_PORT");
+  let port = parseInt(portEnv, 10);
+  if (!Number.isFinite(port) || port < 1 || port > 65535) {
+    throw new Error(`Invalid port in MOZHTTP2_PORT env var: ${portEnv}`);
+  }
+  do_print(`Using HTTP/2 server on port ${port}`);
+  return port;
+}
 
 // Support for making sure we can talk to the invalid cert the server presents
 var CertOverrideListener = function(host, port, bits) {
   this.host = host;
   this.port = port || 443;
   this.bits = bits;
 };
 

--- a/dom/push/test/xpcshell/test_notification_http2.js
+++ b/dom/push/test/xpcshell/test_notification_http2.js
@@ -8,20 +8,17 @@ Cu.import("resource://gre/modules/Servic
 const {PushDB, PushService, PushServiceHttp2} = serviceExports;
 
 var prefs;
 var tlsProfile;
 
 var serverPort = -1;
 
 function run_test() {
-  var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
-  serverPort = env.get("MOZHTTP2_PORT");
-  do_check_neq(serverPort, null);
-  dump("using port " + serverPort + "\n");
+  serverPort = getTestServerPort();
 
   do_get_profile();
   setPrefs({
     'testing.allowInsecureServerURL': true,
   });
   prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
 
   tlsProfile = prefs.getBoolPref("network.http.spdy.enforce-tls-profile");

--- a/dom/push/test/xpcshell/test_register_error_http2.js
+++ b/dom/push/test/xpcshell/test_register_error_http2.js
@@ -9,19 +9,17 @@ const {PushDB, PushService, PushServiceH
 
 var prefs;
 var tlsProfile;
 var serverURL;
 
 var serverPort = -1;
 
 function run_test() {
-  var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
-  serverPort = env.get("MOZHTTP2_PORT");
-  do_check_neq(serverPort, null);
+  serverPort = getTestServerPort();
 
   do_get_profile();
   prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
 
   tlsProfile = prefs.getBoolPref("network.http.spdy.enforce-tls-profile");
 
   serverURL = "https://localhost:" + serverPort;
 

--- a/dom/push/test/xpcshell/test_register_success_http2.js
+++ b/dom/push/test/xpcshell/test_register_success_http2.js
@@ -11,19 +11,17 @@ var prefs;
 var tlsProfile;
 var serverURL;
 var serverPort = -1;
 var pushEnabled;
 var pushConnectionEnabled;
 var db;
 
 function run_test() {
-  var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
-  serverPort = env.get("MOZHTTP2_PORT");
-  do_check_neq(serverPort, null);
+  serverPort = getTestServerPort();
 
   do_get_profile();
   prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
 
   tlsProfile = prefs.getBoolPref("network.http.spdy.enforce-tls-profile");
   pushEnabled = prefs.getBoolPref("dom.push.enabled");
   pushConnectionEnabled = prefs.getBoolPref("dom.push.connection.enabled");
 

--- a/dom/push/test/xpcshell/test_registration_success_http2.js
+++ b/dom/push/test/xpcshell/test_registration_success_http2.js
@@ -16,19 +16,17 @@ PromiseTestUtils.thisTestLeaksUncaughtRe
 
 const {PushDB, PushService, PushServiceHttp2} = serviceExports;
 
 var prefs;
 
 var serverPort = -1;
 
 function run_test() {
-  var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
-  serverPort = env.get("MOZHTTP2_PORT");
-  do_check_neq(serverPort, null);
+  serverPort = getTestServerPort();
 
   do_get_profile();
   prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
 
   run_next_test();
 }
 
 add_task(function* test_pushNotifications() {

--- a/dom/push/test/xpcshell/test_unregister_success_http2.js
+++ b/dom/push/test/xpcshell/test_unregister_success_http2.js
@@ -19,19 +19,17 @@ const {PushDB, PushService, PushServiceH
 var prefs;
 var tlsProfile;
 var pushEnabled;
 var pushConnectionEnabled;
 
 var serverPort = -1;
 
 function run_test() {
-  var env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
-  serverPort = env.get("MOZHTTP2_PORT");
-  do_check_neq(serverPort, null);
+  serverPort = getTestServerPort();
 
   do_get_profile();
   prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
 
   tlsProfile = prefs.getBoolPref("network.http.spdy.enforce-tls-profile");
   pushEnabled = prefs.getBoolPref("dom.push.enabled");
   pushConnectionEnabled = prefs.getBoolPref("dom.push.connection.enabled");