Deleting blank line in code snippet not possible in Firefox

Issue Summary

If you put your cursor on a blank line and hit delete, it doesn't delete that line. This only happens in Firefox. 

Steps to Reproduce

1. In Firefox, open Confluence and create or edit a page. Add the Code snippet macro.
2. Add a few lines of text, and hit enter once to create a blank line.
3. Now try to click delete to go back and delete that line.

Expected Results

The blank line should be deleted after you click delete. Here's how it works in Chrome:

Actual Results

In Firefox, it's not possible to delete that line.

Workaround

Put your cursor at the end of the line before it and hit backspace to delete the line.