Google Docs crashes in Firefox on Windows 10 with your link.
When I re-create the document from scratch, it does not crash.
When I copy the link to my non-crashing document and load it in a new tab, the crash then occurs when I edit the document in the new tab but not when I edit it in the original tab.
No, it's on, just tried it again, got the blue underlines and everything. Original tab doesn't crash, new tabs crash (although I can usually get a few characters in before the crash), once I close the original tab obviously the crashes are permanent.
When I re-create the document from scratch, it does not crash.
When I copy the link to my non-crashing document and load it in a new tab, the crash then occurs when I edit the document in the new tab but not when I edit it in the original tab.