I think version 3.1 is one of those accidental releases that need to be fixed (ie: reverted to how it used to be). Downgrading for now:

(My main problem with this release is the icon is too darned large. It takes up waaaaay too much real-estate.)
https://addons.mozilla.org/en-US/firefox/addon/empty-cache-button/versions/2.7.1-signed.1-signed