diff --git a/uriloader/exthandler/tests/Makefile.in b/uriloader/exthandler/tests/Makefile.in
index d2dcee91501..92f839d5e42 100644
--- a/uriloader/exthandler/tests/Makefile.in
+++ b/uriloader/exthandler/tests/Makefile.in
@@ -52,8 +52,11 @@ MODULE          = test_uriloader_exthandler
 XPCSHELL_TESTS  = unit
 
 ifdef MOZ_IPC
+#FIXME/bug 575918: out-of-process xpcshell is broken on OS X
+ifneq ($(OS_ARCH),Darwin)
 XPCSHELL_TESTS += unit_ipc
 endif
+endif
 
 CPPSRCS =	\
 		WriteArgument.cpp \
diff --git a/uriloader/exthandler/tests/unit_ipc/disable_t_encoding.js b/uriloader/exthandler/tests/unit_ipc/test_encoding.js
similarity index 97%
rename from uriloader/exthandler/tests/unit_ipc/disable_t_encoding.js
rename to uriloader/exthandler/tests/unit_ipc/test_encoding.js
index 9dba572c91e..49630ced79a 100644
--- a/uriloader/exthandler/tests/unit_ipc/disable_t_encoding.js
+++ b/uriloader/exthandler/tests/unit_ipc/test_encoding.js
@@ -86,8 +86,16 @@ DownloadMgrUI.prototype = {
   getAttention: function () { }
 }
 
+function AlertsSVC() { }
+AlertsSVC.prototype = {
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsIAlertsService]),
+  contractID: "@mozilla.org/alerts-service;1",
+  showAlertNotification: function (url, title, text, clickable, cookie, listener, name) { },
+}
+
 registerTemporaryComponent(HelperAppDlg);
 registerTemporaryComponent(DownloadMgrUI);
+registerTemporaryComponent(AlertsSVC);
 
 function initChildTestEnv()
 {