diff --git a/testing/mochitest/browser-test.js b/testing/mochitest/browser-test.js
index d50e8d4a66a..62e8125f47b 100644
--- a/testing/mochitest/browser-test.js
+++ b/testing/mochitest/browser-test.js
@@ -242,10 +242,21 @@ Tester.prototype = {
 
       // Run the test
       this.lastStartTime = Date.now();
-      this.currentTest.scope.test();
+      if ("generatorTest" in this.currentTest.scope) {
+        if ("test" in this.currentTest.scope)
+          throw "Cannot run both a generator test and a normal test at the same time.";
+
+        // This test is a generator. It will not finish immediately.
+        this.currentTest.scope.waitForExplicitFinish();
+        var result = this.currentTest.scope.generatorTest();
+        this.currentTest.scope.__generator = result;
+        result.next();
+      } else {
+        this.currentTest.scope.test();
+      }
     } catch (ex) {
       this.currentTest.addResult(new testResult(false, "Exception thrown", ex, false));
-      this.currentTest.scope.__done = true;
+      this.currentTest.scope.finish();
     }
 
     // If the test ran synchronously, move to the next test, otherwise the test
@@ -354,6 +365,29 @@ function testScope(aTester, aTest) {
     }, Ci.nsIThread.DISPATCH_NORMAL);
   };
 
+  this.nextStep = function test_nextStep(arg) {
+    if (self.__done) {
+      aTest.addResult(new testResult(false, "nextStep was called too many times", "", false));
+      return;
+    }
+
+    if (!self.__generator) {
+      aTest.addResult(new testResult(false, "nextStep called with no generator", "", false));
+      self.finish();
+      return;
+    }
+
+    try {
+      self.__generator.send(arg);
+    } catch (ex if ex instanceof StopIteration) {
+      // StopIteration means test is finished.
+      self.finish();
+    } catch (ex) {
+      aTest.addResult(new testResult(false, "Exception thrown", ex, false));
+      self.finish();
+    }
+  };
+
   this.waitForExplicitFinish = function test_waitForExplicitFinish() {
     self.__done = false;
   };
@@ -393,6 +427,7 @@ function testScope(aTester, aTest) {
 }
 testScope.prototype = {
   __done: true,
+  __generator: null,
   __waitTimer: null,
   __cleanupFunctions: [],
   __timeoutFactor: 1,