Minimal twitter userContent.css....

userContent.css

/* Newtab */
@-moz-document url("about:blank") {
    body {
        background-color: #272b35 !important;
    }
}

@-moz-document url("about:newtab") {
          body {
              background-color: #272b35 !important;
          }
      }


@-moz-document url("https://twitter.com/home") {
    .r-g6ijar, .r-1qk6wnv , .r-1w6e6rj, .r-e7q0ms, .r-1dqbpge, .r-1hycxz, .r-usiww2, .r-15ysp7h, .r-4wgw6l, .r-109y4c4 {
        display: none !important;
    }

    .r-18bvks7, .r-157er04, .r-1ila09b {
        border-color: transparent !important;
        background-color: transparent !important;
    }
    
    .r-obd0qt {
        align-items: flex-start !important;
    }
}