I have the same problem - text is displayed in white, that means I can't read it, which is quite a problem. Besides that, a very helpful tool, if I could just read the text :)

Overall great simple extension for opening Python Notebook files without installing a dedicated application! However it seems that the app is abandoned (Last updated: 2 years ago, Mar 11, 2019). So for that it gets 3 stars, and it is a bit buggy. Namely, some math symbols do not show up properly. Also if you're using a Windows OS and your default theme for apps is 'Dark' the text will show up very light on a light background making it very difficult to read.