--- a/testing/modules/Assert.jsm
+++ b/testing/modules/Assert.jsm
@@ -356,16 +356,30 @@ function expectedException(actual, expec
  *        (mixed) This parameter can be either a RegExp, a function, or a string. The
  *        function is either the error type's constructor, or it's a method that returns a boolean
  *        that describes the test outcome. When string value is provided, it will be used as if it
  *        was provided as the message parameter.
  * @param message (optional)
  *        (string) Short explanation of the expected result
  */
 proto.throws = function(block, expected, message) {
+  // `true` if we realize that we have added an
+  // error to `ChromeUtils.recentJSDevError` and
+  // that we probably need to clean it up.
+  let cleanupRecentJSDevError = false;
+  if ("recentJSDevError" in ChromeUtils) {
+    // Check that we're in a build of Firefox that supports
+    // the `recentJSDevError` mechanism (i.e. Nightly build).
+    if (ChromeUtils.recentJSDevError == undefined) {
+      // There was no previous error, so if we throw
+      // an error here, we may need to clean it up.
+      cleanupRecentJSDevError = true;
+    }
+  }
+
   let actual;
 
   if (typeof expected === "string") {
     message = expected;
     expected = null;
   }
 
   try {
@@ -381,16 +395,28 @@ proto.throws = function(block, expected,
     this.report(true, actual, expected, "Missing expected exception" + message);
   }
 
   if ((actual && expected && !expectedException(actual, expected))) {
     throw actual;
   }
 
   this.report(false, expected, expected, message);
+
+  // Make sure that we don't cause failures for JS Dev Errors that
+  // were expected, typically for tests that attempt to check
+  // that we react properly to TypeError, ReferenceError, SyntaxError.
+  if (cleanupRecentJSDevError && "clearRecentJSDevError" in ChromeUtils) {
+    let recentJSDevError = ChromeUtils.recentJSDevError;
+    if (recentJSDevError) {
+      if (expectedException(recentJSDevError)) {
+        ChromeUtils.clearRecentJSDevError();
+      }
+    }
+  }
 };
 
 /**
  * A promise that is expected to reject:
  * assert.rejects(promise, expected, message);
  *
  * @param promise
  *        (promise) A promise that is expected to reject