@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain(mail.google.com) {
div[class^=yxEQwb] {display: none !important;}
div[class='XoqCub a3hTGd'] {display: none !important;}
div[class='XoqCub I94Sdc'] {display: none !important;}
div[class='XoqCub V3vJRb'] {display: none !important;}

/* The line below should be modified. */
/* I have 1280x768 screen & 970px is OK for me. */
/* You should find your best value. */

div[class='XoqCub ice3Ad'] {width: 970px !important;}
}