It’s a new feature of ‘Missing e’
it’s killing me. HOW ARE YOU DOING THAT?
It’s a new feature of Missing e, in version 1.5.7, that allows you to magnify Tumblr avatar images. It is in the Magnifier feature but it isn’t enabled by default. You have to turn it on in the settings.
Note that it works on avatars next to posts, and notifications and also in your followers/following lists.