I'll add: Press ? to view the keyboard shortcuts.

> Press I in a PR to hide comments.

Thank you! Comments can make it impossible to read the diff. And considering that by default anyone can post comments anywhere, this can be a serious issue. The other tips weren't that useful for me, but this one is a true gem (and is fairly well hidden -- no UI and hard to find in the docs; however when I pressed "?" it was listed in the keyboard shortcuts, which is actually how I discovered "?").