Put this somewhere in your User Stylesheets file for Google Chrome and Yahoo Mail will be *so much better*.

FixYahoo.css

div#main > div#paneshell > div#shellcontent { right: 0 !important; }
div#main > div#toolbar.fresh-toolbar { right: 0 !important; }
.yucs-fl-left > div#yucs-nav.yui3-menu { display: none; }
.yucs-fl-left > div#yucs-logo { display: none; }
div#yucs-prop_search_button_wrapper.yucs-search-buttons { display: none !important; }
div#yucs-web_search_button_wrapper.yucs-search-buttons { display: none !important; }
div#yucs.yucs-mc > div.yucs-fl-right > div#yucs-network_link { display: none !important; }
.yucs-form-input > input#mnp-search_box.yucs-search-input {
	border-radius: 0 !important;
	border: 1px solid #451A87 !important;
	-webkit-box-shadow: 0 0 0 1px #9A7BC9 inset !important;
	background: right -745px url('http://mail.yimg.com/ok/u/assets/sprite/default/16x16/common-leftrail-ltr-68317.png') no-repeat content-box,
				linear-gradient(to bottom, #351B5C 0, #61399d 10%, #734FAB 100%) !important;
	height: 24px !important;
	background-position: 10px 0;
}
.yucs-form-input > input#mnp-search_box.yucs-search-input:focus {
	border: 1px solid #333 !important;
	-webkit-box-shadow: 0 0 0 1px #FFF inset !important;
	background: right -745px url('http://mail.yimg.com/ok/u/assets/sprite/default/16x16/common-leftrail-ltr-68317.png') no-repeat content-box,
				linear-gradient(to bottom, #EEE 0, #F0F0F0 10%, #F8F8F8 100%) !important;
}
div#yucs.yucs-mc {
	padding: 0 !important;
}
div#yucs.yucs-mc > div.yucs-fl-left {
	float: none !important;
	position: absolute !important;
	width: auto !important;
	margin: 0 !important;
	right: 1px;
	left: 800px !important;
	top: 41px;
}
div#yucs.yucs-mc > div.yucs-fl-left > div#yucs-search {
	width: 100% !important;
	max-width: 100% !important;
	margin: 0 !important;
}
div#yucs-search > form.yucs-search > table {
	height: auto !important;
}
div.nav-bar[id^=yui] > div.tabs[id^=yui] {
	padding-left: 10px !important;
}
div#yucs.yucs-mc > div.yucs-fl-right {
	margin: 5px 10px !important;
}
div#yucs.yucs-mc > div.yucs-fl-right > div#yucs-profile {
	margin-top: 0px !important;
}
div#yucs.yucs-mc > div.yucs-fl-right > div#yucs-help {
	margin-top: 0px !important;
}
a#yucs-menu_link_profile_signed_out,
a#yucs-menu_link_profile,
div.yucs-profile div.yui3-menu-label {
	min-height: auto !important;
}
a.yucs-submenu-toggle > span.yucs-avatar {
	height: 28px !important;
	margin-bottom: 0 !important;
}
div#yucs-help a#yucs-help_button {
	margin: 0 !important;
}
body.panescroll.uh3.mf.mas > div.nav-bar {
	top: 0 !important;
	margin-right: 180px !important;
	width: auto !important;
}
iframe#tictac_xdm { visibility: hidden !important; }
div#main[role=tabpanel] {
	top: 38px !important;
}
div#main > div#paneshell > div#shellcontent,
div#main > div#paneshell > div#shellnavigation {
	top: 72px !important;
}
body.panescroll.tictac-dark-theme.mf.mas {
	overflow: hidden !important;
}