"Download THIS Notebook!" doesn't work in Firefox

[jonmmease]

To reproduce:

• Visit: https://plot.ly/python/line-and-scatter/ using Chrome
• Click "Downdload THIS Notebook!" button, and you will navigate to the notebook from the notebook_demo account.
• Visit the same link from Firefox (I'm on 61.0.2 (64-bit) on MacOS)
• Click the same button and nothing happens. Firefox doesn't respond as if it's trying to load anything.

[nicolaskruchten]

We'll clear this up when we do #1501