v1.2.x: cloning error when opening files from large repositories in Firefox

[musicog]

This ticket documents a known issue with the new git implementation (mei-friend v1.2.0) in Firefox:

Attempting to open encodings from large repositories (> ~450MB) may cause a 'cloning error' pop-up to display instead of the requested encoding. This appears to be an issue with the underlying isomorphic-git module; we are currently waiting on clarification and hoping this can be fixed.

TypeError: null has no properties
    readSlice http://localhost:5001/static/deps/isomorphic-git.umd.min.js:8

As a work-around when working with such large repositories and encountering this problem, either

1. switch to another browser such as Chrome to work on encodings from such large repositories; or,
2. download the encoding locally onto your machine, perform your edits, and then save locally and upload to Github outside of mei-friend to commit your changes