Sometimes a PR gets lots of comments at the top and finding the list of changed files becomes difficult. If you could show a button somewhere that is always in the same place and visible when the list is not, that would be awesome.
I'm thinking something like this (run from a JS console while on a PR):
$('#repo-content').append('<div id="file-list-div" style="position: fixed; top: 10px; right: 10px; border: 1px solid rgb(204, 204, 204); padding: 5px; background-color: white;"><a href="#pullrequest-diff">File List</a></div>');
Attachment shows how this looks (I added some coloring).