Cannot open large files

Opening a large file (100 MB) does not work:
- run jupyter notebook
- open file (download 'CRM_RandomForest.ipynb' file from here: https://notebooks.azure.com/rashaf/libraries/github475-Rlib)
- page never loads any content and becomes unresponsive

Found through Azure Notebooks but confirmed to repro when running notebooks locally: https://github.com/Microsoft/AzureNotebooks/issues/475

After opening the file in a text editor and stripping out the output, the notebook can be opened fine.

Reproduce the issue by running `jupyter notebook` and opening `CRM_RandomForest.ipynb`, using the linked Azure Notebooks source if needed. Compare the behavior with the same notebook after its output is stripped. Done means the original large notebook opens and the page remains responsive.

Written by the indexing model from the issue text.