An Ext JS 4.1 link button. It is a button, styled as a link.

LinkButton.css

button.linkButton {
	overflow:visible; /* Shrinkwrap the text in IE7- */
	margin:0;
	padding:0;
	border:0;
	color: #2B547D;
	background:transparent;
	font:inherit !important; /* Inherit font settings (doesn’t work in IE7-) */
	line-height:normal; /* Override line-height to avoid spacing issues */
	text-decoration:underline; /* Make it look linky */
	cursor:pointer; /* Buttons don’t make the cursor change in all browsers */
	-moz-user-select:text; /* Make button text selectable in Gecko */
}

/* Remove mystery padding in Gecko browsers.
 * See https://bugzilla.mozilla.org/show_bug.cgi?id=140562
 */
button.linkButton::-moz-focus-inner {
	padding:0;
	border:0;
}

LinkButton.js

Ext.define('LinkButton', {
	extend:'Ext.Component',
	alias:'widget.linkbutton',

	childEls:[
		'btnEl'
	],
	renderTpl:['<button id="{id}-btnEl" type="button" class="linkButton"',
		   '<tpl if="fontSize"> style="font-size:{fontSize}"</tpl>',
		   '<tpl if="tabIndex"> tabIndex="{tabIndex}"</tpl>',
		   '>{text}</button>'
		  ],

	/**
	 * @cfg {String} text
	 * The text to be used as innerHTML.
	 */

	/**
	 * @cfg {Number} tabIndex
	 * Set a DOM tabIndex for this button.
	 */

	/**
	 * @cfg {String} fontSize
	 * Sets the font-size on the button.  Must be in a valid format like "11px".  Really
	 * only needed if supporting IE7.
	 */

	config:{
		handler:function () {
		}
	},
	initComponent:function () {
		var me = this;
		me.callParent(arguments);
	},
	beforeRender:function () {
		var me = this;
		Ext.applyIf(me.renderData, {
			text:me.text || '',
			tabIndex: me.tabIndex,
			fontSize: me.fontSize
		});
	},
	onRender:function (ct, position) {
		var me = this,
		    btn;
		me.callParent(arguments);

		btn = me.btnEl;
		me.mon(btn, 'click', me.onClick, me);
	},
	onClick:function (e) {
		var me = this;
		if (me.preventDefault || (me.disabled && me.getHref()) && e) {
			e.preventDefault();
		}
		if (e.button !== 0) {
			return;
		}
		if (!me.disabled) {
			me.fireHandler(e);
		}
	},
	fireHandler:function (e) {
		var me = this,
		    handler = me.handler;

		me.fireEvent('click', me, e);
		if (handler) {
			handler.call(me.scope || me, me, e);
		}
	},

	setText:function (text) {
		var me = this;
		me.text = text;
		if (me.rendered) {
			me.btnEl.update(text || '');
			me.updateLayout();
		}
	}
});

Added tabIndex and fontSize to the config options.