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st0n3 / Fastmail - always show email details 

// ==UserScript==
// @name        Fastmail - always show email details
// @namespace   ston3.uk
// @description Auto show the email message header details
// @include     https://www.fastmail.com/*
// @version     1
// @grant       none
// ==/UserScript==

var style = document.createElement("style");
style.innerHTML = ".v-Message-details { height: auto; } .v-MessageCard-toggleDetails {display:none;}";
document.body.appendChild(style);