MS Edge (non-Chromium): jupyter-matplotlib plots not showing in JupyterLab

Nobody has claimed this yet.

Hello, this is my first GitHub post. I just installed ipympl and can't get it to work properly in JupyterLab. The widget controls are there, but plot is blank. Plot coordinates are updated when mouse is moved around in the plot area. It works fine in Jupyter notebooks.

Setup (Win 10 x64, Anaconda):

```
conda list jupyter
# packages in environment at C:\Users\me\Anaconda3\envs\jupmpl:
#
# Name Version Build Channel
jupyter 1.0.0 py37_7
jupyter_client 5.3.4 py37_0
jupyter_console 6.1.0 py_0
jupyter_core 4.6.1 py37_0
jupyterlab 1.2.6 pyhf63ae98_0
jupyterlab_server 1.0.6 py_0
jupyterthemes 0.20.0 pypi_0 pypi
```

```
jupyter labextension list
JupyterLab v1.2.6
Known labextensions:
app dir: C:\Users\me\Anaconda3\envs\jupmpl\share\jupyter\lab
@bokeh/jupyter_bokeh v1.1.1 enabled ok
@jupyter-widgets/jupyterlab-manager v1.1.0 enabled ok
jupyter-matplotlib v0.5.0 enabled ok
```

```
conda -V
conda 4.8.2
```

```
conda list 'python|conda|ipympl|nodejs|ipywidgets|widgetsnbextension|notebook|matplotlib'
# packages in environment at C:\Users\me\Anaconda3\envs\jupmpl:
#
# Name Version Build Channel
_anaconda_depends 2019.03 py37_0
anaconda custom py37_1
anaconda-client 1.7.2 py37_0
anaconda-navigator 1.9.7 py37_0
anaconda-project 0.8.4 py_0
conda-package-handling 1.6.0 py37h62dcd97_0
conda-verify 3.4.2 py_1
ipympl 0.4.1 py_0 conda-forge
ipython 7.12.0 py37h5ca1d4c_0
ipython_genutils 0.2.0 py37_0
ipywidgets 7.5.1 py_0
matplotlib 3.1.3 py37_0
matplotlib-base 3.1.3 py37h64f37c6_0
msgpack-python 0.6.1 py37h74a9793_1
msys2-conda-epoch 20160418 1
nodejs 13.8.0 0 conda-forge
notebook 6.0.3 py37_0
python 3.7.6 h60c2a47_2
python-dateutil 2.8.1 py_0
python-libarchive-c 2.8 py37_13
widgetsnbextension 3.5.1 py37_0

```

I followed install directions as on the jupyterlab-matplotlib GitHub site, and am using the matplotlib Jupyter magic:

**%matplotlib widget**


Note that I can get working interactive 3d plots in external windows by invoking **%pylab** or
**%matplotlib** from JupyterLab. But I get no plots inline.

I have messed around with this for many hours and am getting nowhere. Any help would be greatly appreciated! :-)

Start by reproducing the blank inline plot in JupyterLab 1.2.6 on non-Chromium Microsoft Edge using the reported ipympl, matplotlib, and jupyter-matplotlib versions. Compare the same %matplotlib widget example in Jupyter Notebook and inspect the JupyterLab extension and widget rendering path. Done means the plot renders inline with working controls in the affected environment.

Written by the indexing model from the issue text.