Mark a bunch of tests as passing now that stack_trace works with the new Firefox.

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index f71ed94f82336efc1eeed5241cf52bacdc09f769..592f3376994a42943cbd3011b6bc8e3b0a2223b6 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -113,22 +113,6 @@ observe/test/unique_message_test: Skip # Intended only as a vm test.
 polymer/test/build/unique_message_test: Skip # Intended only as a vm test.
 code_transformers/test/unique_message_test: Skip # Intended only as a vm test.
 
-[ $compiler == dart2js && $runtime == ff ]
-scheduled_test/test/unittest_compatibility_test: RuntimeError # Issue 20989
-
-[ $compiler == dart2js && $runtime == ff && $system == windows ]
-http/test/html/client_test: Fail # Issue 19750
-scheduled_test/test/scheduled_stream/scheduled_stream_test: Fail # Issue 19750
-json_rpc_2/test/server/server_test: Fail # Issue 19750
-shelf/test/log_middleware_test: Fail # Issue 19750
-
-[ $runtime == ff ]
-stack_trace/test/trace_test: Fail # Issue 19750
-http/test/html/client_test: Fail # Issue 19750
-scheduled_test/test/scheduled_stream/scheduled_stream_test: Fail # Issue 19750
-json_rpc_2/test/server/server_test: Fail # Issue 19750
-shelf/test/log_middleware_test: Fail # Issue 19750
-
 [ $compiler == dart2js && $checked ]
 crypto/test/base64_test: Slow, Pass