During the back and forth of reviewing a large pull request, it's easy to lose track of what you've already reviewed and what you haven't. This extension adds a new button to the header of each file in a pull request that allows you to toggle the reviewed/unreviewed status of that file. If the file is later updated or commented on after you've marked it as reviewed, it will revert to the unreviewed state. This makes it much easier to focus on only the files that need your attention.

Head over to the Chrome web store or Firefox Addons to install it.