How to tweak FastMail web-interface

It is a very short note as I simply want to share my personal CSS modifications to the FastMail web-interface
using Stylish a user styles manager

CSS style modification

@namespace url(;
@-moz-document domain("") {
  .v-Thread {
    max-width: none;
  .app-contentCard, .v-SelectedConversations {
    max-width: none;
  #compose .v-Compose {
    max-width: none;


Notice that now it nicely fits Full HD resolution.

FastMail - Conversation view

FastMail - Selected conversations

FastMail - Compose message

Simple as that.