navigator should scroll horizontally, and show both horizontal and vertical scrollbars

[maltenuhn]

MN: I've tried to tweak this in the browser devtools, and it does not appear to be a trivial change. It's not absolutely critical because we can resize the navigator

[maltenuhn]

@liady I'm assigning this to you in the hope that it will be trivial for you (since you actually know about these things :)