Page "times out" and comments cannot be posted

Summary

This has been happening for a while now, but new behavior has made it very tedious. When creating a comment on a page which has been open for some time (~30 minutes I'd say), trying to make a comment causes an error banner to appear:

Your comment could not be submitted! Please check your network connection and try again.

Refreshing the page "fixes" this. However, recently (since maybe 9.3 or so), my comment text is now getting HTML-escaped for any special characters (such as ', a backtick, etc.) which is extremely tedious to undo.

I'm using Firefox 55 on Linux and tend to block third-party communications. I've seen it both on gitlab.com as well as our deployment.

Steps to reproduce

Leave a page open for a while and try to post a comment.

Example Project

I suspect this is more a browser-related problem.

What is the current bug behavior?

The network connection is "lost" . When the error box appears, the comment text gets HTML-escaped.

What is the expected correct behavior?

Don't lose the network connection. Especially don't HTML-escape the comment text.

Possible fixes

Looks like it could be related to getFormData in notes.js.