Bug report

Bug summary

using "%matplotlib notebook" to get interactive plots in notebook running on firefox browser stopped working upon upgrade from matplotlib 3.1.1 to 3.3.1. Firefox 68.0.1 (64-bit) for Linux MINT.

Still works fine in google chrome. Other interactive like "%matplotlib widget" or "%matplotlib ipympl" are OK in both firefox & chrome.

No error message, just a small triangle appears in lieu if the plot in the notebook.

Code for reproduction

# Paste your code here
%matplotlib notebook
import matplotlib
import matplotlib.pyplot as plt
fig,ax=plt.subplots()
ax.plot([0,1,2],[1.1,2.3,4],'o');
print(matplotlib.__version__)
#
#

Actual outcome

# If applicable, paste the console output here
#
#

Expected outcome

Used to work in matplotlib 3.1.1

Matplotlib version

• Operating system: Linux MINT

• Matplotlib version: 3.3.1

• Matplotlib backend (print(matplotlib.get_backend())): nbAgg

• Python version: 3.7.8 | packaged by conda-forge

• Jupyter version (if applicable):
  jupyter core : 4.6.3
  jupyter-notebook : 6.1.4
  qtconsole : 4.7.5
  ipython : 7.17.0
  ipykernel : 5.3.4
  jupyter client : 6.1.6
  jupyter lab : not installed
  nbconvert : 5.6.1
  ipywidgets : 7.5.1
  nbformat : 5.0.7
  traitlets : 4.3.3

• Other libraries:

install from conda

channels:

• gimli
• anaconda
• conda-forge
• defaults