There are a few updates coming in today, and I'm going to make separate posts for each of them. This is the first one, added by James Southern (I don't know if he wants his Tildes account named) as an open-source contribution:
Your unread notifications page now has a "Mark all read" button at the top, just to the right of the title. Clicking it will mark all notifications on the page as read so that you don't need to do them each individually.
It works in a way that makes sure that it only marks ones that are on the page, and won't affect any new ones that came in after the page was loaded. If you have the "Automatically mark all notifications read when you view the Unread Notifications page" setting enabled, it won't show up (because you don't need it).
Please post with any feedback or issues you notice with it. Thanks, James!