if(navigator.userAgent.indexOf("MSIE") > -1){ //Internet Explorer 
document.write('<!-'+'-[if IE]>');  
document.write('<input type="image" src="http://eizou-onkyo.com/img/bookmark.gif"'); 
document.write(' onclick="window.external.AddFavorite(\'http://eizou-onkyo.com/\',\'業務用映像・音響機器市場\')">'); 
document.write('<![endif]-'+'->'); 
} 

else if(navigator.userAgent.indexOf("Firefox") > -1){ //Firefox  
 
} 
else if(navigator.userAgent.indexOf("Opera") > -1){ //Opera 
document.write('<a href="http://eizou-onkyo.com/" rel="sidebar" title="業務用映像・音響機器市場"><img src="http://eizou-onkyo.com/img/bookmark.gif" /></a>'); 
}

else { //該当なし 
void(0); //何もしない 

}