getpass() not working in Firefox 65.0

Using Firefox 65.0, the `getpass()` function is not working. To reproduce the problem, just create a notebook with and execute the following:

`import getpass`
`a = getpass.getpass()`

Enter any characters in the input field, press enter and nothing will happen. If you use `input()` it will work correctly. I traced back the error to the following line:

https://github.com/jupyter/notebook/blob/132f27306522b32fa667a6b208034cb7a04025c9/notebook/static/notebook/js/outputarea.js#L942

In Firefox 65.0, the keycode returned for a password field is always 229. This problem does not happen in Chrome.

Reproduce the issue in a notebook with Firefox 65.0 using the getpass() example, then inspect notebook/static/notebook/js/outputarea.js at line 942. Done means pressing Enter after entering a password submits the getpass prompt in Firefox while input() continues to work.

Written by the indexing model from the issue text.