How can I get old matplotlib version 1.5.1 interface?

Question

I recently updated from matplotlib 1.5.1 to 2.2.3 with

$ pip install -U matplotlib

When showing plotted data with

>>> plt.show()

I could see plots displayed as shown in the attached picture "Output before update" before running the update from 1.5.1 to 2.2.3. Because I didn't like the new interface of version 2.2.3 when displaying plots I switched back to the old version with

$ pip install matplotlib==1.5.1

Yet I'm still seeing a different interface when I show plots using the old matplotlib version (as you can see in the image "Output after update and return to the old version"), even though I returned to the old version of matplotlib I had used to generate the "Output before update".

You can check what I mean by "interface" when you type in your command line:

$ python
>>> import matplotlib.pyplot as plt
>>> plt.plot()
>>> plt.show()

You'll see the "interface" (in my case IPython) and an empty plot.

My questions are: How do I display plots with the old output window again ("Output before update", see below)? And why didn't the return to version 1.5.1 bring the old output window back as well?

Attached you find a comparison between the old output interface that I'd like to get back, and the new output using the same matplotlib version (slightly different data shown, but both plotted in default style, only with colors and markers manually set). The new output is blurry and thick, and the data points are very large as opposed to the old version, which I find much less aesthetic.

Output after update and return to the old version

Output before update

Picture of the "blurry" output window