diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 3a1a5121c9..5881c64da3 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -36,7 +36,8 @@ jobs:
         python -m sphinx -T -E -b html -d ../build/doctrees -D language=en . ../build/html
   js:
     name: JavaScript
-    runs-on: ubuntu-latest
+    # as of #3653 ubuntu-latest wasn't working
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v2
@@ -50,7 +51,6 @@ jobs:
           **/requirements*.txt
     - name: Install dependencies
       run: |
-        sudo apt-get install -y firefox
         python -m pip install --upgrade pip
         python -m pip install jupyterlab~=3.0
     - name: Install node
diff --git a/python/ipywidgets/ipywidgets/widgets/tests/test_send_state.py b/python/ipywidgets/ipywidgets/widgets/tests/test_send_state.py
index a39252319e..ec18ae4af1 100644
--- a/python/ipywidgets/ipywidgets/widgets/tests/test_send_state.py
+++ b/python/ipywidgets/ipywidgets/widgets/tests/test_send_state.py
@@ -12,29 +12,20 @@
 # A widget with simple traits
 class SimpleWidget(Widget):
     a = Bool().tag(sync=True)
-    b = Tuple(Bool(), Bool(), Bool(), default_value=(False, False, False)).tag(sync=True)
+    b = Tuple(Bool(), Bool(), Bool(), default_value=(False, False, False)).tag(
+        sync=True
+    )
     c = List(Bool()).tag(sync=True)
 
+
 def test_empty_send_state():
     w = SimpleWidget()
     w.send_state([])
     assert w.comm.messages == []
 
+
 def test_empty_hold_sync():
     w = SimpleWidget()
     with w.hold_sync():
         pass
     assert w.comm.messages == []
-
-
-def test_control():
-    comm = DummyComm()
-    Widget.close_all()
-    w = SimpleWidget()
-    Widget.handle_control_comm_opened(
-        comm, dict(metadata={'version': __control_protocol_version__})
-    )
-    Widget._handle_control_comm_msg(dict(content=dict(
-        data={'method': 'request_states'}
-    )))
-    assert comm.messages
diff --git a/python/ipywidgets/ipywidgets/widgets/tests/test_widget.py b/python/ipywidgets/ipywidgets/widgets/tests/test_widget.py
index 065aa1fc67..7f7425a9b9 100644
--- a/python/ipywidgets/ipywidgets/widgets/tests/test_widget.py
+++ b/python/ipywidgets/ipywidgets/widgets/tests/test_widget.py
@@ -3,16 +3,18 @@
 
 """Test Widget."""
 
+import inspect
+
+import pytest
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.display import display
 from IPython.utils.capture import capture_output
-import inspect
-import pytest
 
 from .. import widget
 from ..widget import Widget
 from ..widget_button import Button
 
+
 def test_no_widget_view():
     # ensure IPython shell is instantiated
     # otherwise display() just calls print
@@ -24,10 +26,12 @@ def test_no_widget_view():
 
     assert len(cap.outputs) == 1, "expect 1 output"
     mime_bundle = cap.outputs[0].data
-    assert mime_bundle['text/plain'] == repr(w), "expected plain text output"
-    assert 'application/vnd.jupyter.widget-view+json' not in mime_bundle, "widget has no view"
-    assert cap.stdout == '', repr(cap.stdout)
-    assert cap.stderr == '', repr(cap.stderr)
+    assert mime_bundle["text/plain"] == repr(w), "expected plain text output"
+    assert (
+        "application/vnd.jupyter.widget-view+json" not in mime_bundle
+    ), "widget has no view"
+    assert cap.stdout == "", repr(cap.stdout)
+    assert cap.stderr == "", repr(cap.stderr)
 
 
 def test_widget_view():
@@ -41,10 +45,12 @@ def test_widget_view():
 
     assert len(cap.outputs) == 1, "expect 1 output"
     mime_bundle = cap.outputs[0].data
-    assert mime_bundle['text/plain'] == repr(w), "expected plain text output"
-    assert 'application/vnd.jupyter.widget-view+json' in mime_bundle, "widget should have have a view"
-    assert cap.stdout == '', repr(cap.stdout)
-    assert cap.stderr == '', repr(cap.stderr)
+    assert mime_bundle["text/plain"] == repr(w), "expected plain text output"
+    assert (
+        "application/vnd.jupyter.widget-view+json" in mime_bundle
+    ), "widget should have have a view"
+    assert cap.stdout == "", repr(cap.stdout)
+    assert cap.stderr == "", repr(cap.stderr)
 
 
 def test_close_all():
diff --git a/python/ipywidgets/ipywidgets/widgets/widget.py b/python/ipywidgets/ipywidgets/widgets/widget.py
index 4f4dcb3732..030fdc45ce 100644
--- a/python/ipywidgets/ipywidgets/widgets/widget.py
+++ b/python/ipywidgets/ipywidgets/widgets/widget.py
@@ -418,7 +418,7 @@ def handle_comm_opened(comm, msg):
         state = data['state']
 
         # Find the widget class to instantiate in the registered widgets
-        widget_class = register.get(state['_model_module'],
+        widget_class = _registry.get(state['_model_module'],
                                                state['_model_module_version'],
                                                state['_model_name'],
                                                state['_view_module'],