Stack Snippets do not load in the SE editor

[ETHproductions]

When writing/editing a question/answer while the userscript is turned on, the Stack Snippet icon does not appear in the toolbar, nor do existing Stack Snippets render as they should (they just appear as code blocks). Snippets do render properly in answers that are not being edited. Everything works fine when the userscript is turned off.

I have a hunch that this is related to #124...

Tested in Firefox 54 on Windows 7