--- a/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js
+++ b/toolkit/components/crashes/tests/xpcshell/test_crash_manager.js
@@ -32,17 +32,17 @@ add_task(async function test_constructor
     storeDir: "/baz",
   });
   Assert.ok(m, "CrashManager can be created.");
 });
 
 add_task(async function test_constructor_invalid() {
   Assert.throws(() => {
     new CrashManager({foo: true});
-  });
+  }, /Required key not present in options/);
 });
 
 add_task(async function test_get_manager() {
   let m = await getManager();
   Assert.ok(m, "CrashManager obtained.");
 
   await m.createDummyDump(true);
   await m.createDummyDump(false);
@@ -648,9 +648,8 @@ add_task(async function test_telemetryHi
 
   // Check that we have the expected keys.
   let snap = h.snapshot();
   Assert.equal(Object.keys(snap).length, keysCount,
     "Some crash types have not been recorded, see the list in Histograms.json");
   Assert.deepEqual(Object.keys(snap).sort(), keys.sort(),
     "Some crash types do not match");
 });
-

--- a/toolkit/components/mozintl/test/test_mozintl_getLocaleDisplayNames.js
+++ b/toolkit/components/mozintl/test/test_mozintl_getLocaleDisplayNames.js
@@ -39,45 +39,45 @@ add_test(function test_other_subtags_ign
   deepEqual(gLocDN(["en-t-en-latn"]), ["English"]);
   deepEqual(gLocDN(["en-u-hc-h24"]), ["English"]);
   run_next_test();
 });
 
 add_test(function test_invalid_locales() {
   deepEqual(gLocDN(["2"]), ["2"]);
   deepEqual(gLocDN([""]), [""]);
-  Assert.throws(() => gLocDN([2]));
-  Assert.throws(() => gLocDN([{}]));
-  Assert.throws(() => gLocDN([true]));
+  Assert.throws(() => gLocDN([2]), /All locale codes must be strings/);
+  Assert.throws(() => gLocDN([{}]), /All locale codes must be strings/);
+  Assert.throws(() => gLocDN([true]), /All locale codes must be strings/);
   run_next_test();
 });
 
 add_test(function test_language_only() {
   deepEqual(gLangDN([]), []);
   deepEqual(gLangDN(["en"]), ["English"]);
   deepEqual(gLangDN(["und"]), ["und"]);
   run_next_test();
 });
 
 add_test(function test_invalid_languages() {
   deepEqual(gLangDN(["2"]), ["2"]);
   deepEqual(gLangDN([""]), [""]);
-  Assert.throws(() => gLangDN([2]));
-  Assert.throws(() => gLangDN([{}]));
-  Assert.throws(() => gLangDN([true]));
+  Assert.throws(() => gLangDN([2]), /All language codes must be strings/);
+  Assert.throws(() => gLangDN([{}]), /All language codes must be strings/);
+  Assert.throws(() => gLangDN([true]), /All language codes must be strings/);
   run_next_test();
 });
 
 add_test(function test_region_only() {
   deepEqual(gRegDN([]), []);
   deepEqual(gRegDN(["US"]), ["United States"]);
   deepEqual(gRegDN(["und"]), ["UND"]);
   run_next_test();
 });
 
 add_test(function test_invalid_regions() {
   deepEqual(gRegDN(["2"]), ["2"]);
   deepEqual(gRegDN([""]), [""]);
-  Assert.throws(() => gRegDN([2]));
-  Assert.throws(() => gRegDN([{}]));
-  Assert.throws(() => gRegDN([true]));
+  Assert.throws(() => gRegDN([2]), /All region codes must be strings/);
+  Assert.throws(() => gRegDN([{}]), /All region codes must be strings/);
+  Assert.throws(() => gRegDN([true]), /All region codes must be strings/);
   run_next_test();
 });

--- a/toolkit/components/normandy/test/unit/test_Sampling.js
+++ b/toolkit/components/normandy/test/unit/test_Sampling.js
@@ -19,17 +19,18 @@ add_task(async function testBucketSample
 
   // Known samples. The numbers are nonces to make the tests pass
   equal(await Sampling.bucketSample("test-0", 0, 5, 10), true, "bucketSample returns true for known matching sample");
   equal(await Sampling.bucketSample("test-1", 0, 5, 10), false, "bucketSample returns false for known non-matching sample");
 });
 
 add_task(async function testRatioSample() {
   // Invalid input
-  Assert.rejects(Sampling.ratioSample("test", []), "ratioSample rejects for a list with no ratios");
+  await Assert.rejects(Sampling.ratioSample("test", []), /ratios must be at least 1 element long/,
+                       "ratioSample rejects for a list with no ratios");
 
   // Absolute samples
   equal(await Sampling.ratioSample("test", [1]), 0, "ratioSample returns 0 for a list with only 1 ratio");
   equal(
     await Sampling.ratioSample("test", [0, 0, 1, 0]),
     2,
     "ratioSample returns the only non-zero bucket if all other buckets are zero"
   );

--- a/toolkit/components/osfile/tests/xpcshell/test_remove.js
+++ b/toolkit/components/osfile/tests/xpcshell/test_remove.js
@@ -16,16 +16,17 @@ function run_test() {
   run_next_test();
 }
 
 add_task(async function test_ignoreAbsent() {
   let absent_file_name = "test_osfile_front_absent.tmp";
 
   // Removing absent files should throw if "ignoreAbsent" is true.
   await Assert.rejects(OS.File.remove(absent_file_name, {ignoreAbsent: false}),
+                       err => err.operation == "remove",
                        "OS.File.remove throws if there is no such file.");
 
   // Removing absent files should not throw if "ignoreAbsent" is true or not
   // defined.
   let exception = null;
   try {
     await OS.File.remove(absent_file_name, {ignoreAbsent: true});
     await OS.File.remove(absent_file_name);
@@ -35,16 +36,17 @@ add_task(async function test_ignoreAbsen
   Assert.ok(!exception, "OS.File.remove should not throw when not requested.");
 });
 
 add_task(async function test_ignoreAbsent_directory_missing() {
   let absent_file_name = OS.Path.join("absent_parent", "test.tmp");
 
   // Removing absent files should throw if "ignoreAbsent" is true.
   await Assert.rejects(OS.File.remove(absent_file_name, {ignoreAbsent: false}),
+                       err => err.operation == "remove",
                        "OS.File.remove throws if there is no such file.");
 
   // Removing files from absent directories should not throw if "ignoreAbsent"
   // is true or not defined.
   let exception = null;
   try {
     await OS.File.remove(absent_file_name, {ignoreAbsent: true});
     await OS.File.remove(absent_file_name);

--- a/toolkit/components/passwordmgr/test/unit/test_logins_change.js
+++ b/toolkit/components/passwordmgr/test/unit/test_logins_change.js
@@ -293,17 +293,17 @@ add_task(function test_modifyLogin_nsIPr
                 /No matching logins/);
 
   // It is also possible to provide no properties to be modified.
   Services.logins.modifyLogin(updatedLoginInfo, newPropertyBag());
 
   // Specifying a null property for a required value should throw.
   Assert.throws(() => Services.logins.modifyLogin(loginInfo, newPropertyBag({
     usernameField: null,
-  })));
+  })), /No matching logins/);
 
   // The login can be changed to have a different type and hostname.
   Services.logins.modifyLogin(updatedLoginInfo, differentLoginProperties);
   LoginTestUtils.checkLogins([differentLoginInfo]);
 
   // It is now possible to add a login with the old type and hostname.
   Services.logins.addLogin(loginInfo);
   LoginTestUtils.checkLogins([loginInfo, differentLoginInfo]);

--- a/toolkit/modules/tests/xpcshell/test_Integration.js
+++ b/toolkit/modules/tests/xpcshell/test_Integration.js
@@ -201,17 +201,17 @@ add_task(async function test_state_prese
  * This is limited by the fact that interfaces with the "[function]" annotation,
  * for example nsIObserver, do not call the QueryInterface implementation.
  */
 add_task(async function test_xpcom_throws() {
   let combined = Integration.testModule.getCombined(TestIntegration);
 
   // This calls QueryInterface because it looks for nsISupportsWeakReference.
   Assert.throws(() => Services.obs.addObserver(combined, "test-topic", true),
-                "NS_NOINTERFACE");
+                /NS_NOINTERFACE/);
 });
 
 /**
  * Checks that getters defined by defineModuleGetter are able to retrieve the
  * latest version of the combined integration object.
  */
 add_task(async function test_defineModuleGetter() {
   let objectForGetters = {};

--- a/toolkit/modules/tests/xpcshell/test_timer.js
+++ b/toolkit/modules/tests/xpcshell/test_timer.js
@@ -97,25 +97,25 @@ add_task(async function test_setInterval
       }
       calls++;
     }, 100, target, 15, "hola");
   });
 });
 
 add_task(async function test_setTimeoutNonFunction() {
   Assert.throws(() => { imported.setTimeout({}, 0); },
-                "callback is not a function in setTimeout");
+                /callback is not a function in setTimeout/);
 });
 
 add_task(async function test_setIntervalNonFunction() {
   Assert.throws(() => { imported.setInterval({}, 0); },
-                "callback is not a function in setInterval");
+                /callback is not a function in setInterval/);
 });
 
 add_task(async function test_setTimeoutWithTargetNonFunction() {
   Assert.throws(() => { imported.setTimeoutWithTarget({}, 0); },
-                "callback is not a function in setTimeout");
+                /callback is not a function in setTimeout/);
 });
 
 add_task(async function test_setIntervalWithTargetNonFunction() {
   Assert.throws(() => { imported.setIntervalWithTarget({}, 0); },
-                "callback is not a function in setInterval");
+                /callback is not a function in setInterval/);
 });