If you don't like that microscopic default icon, this is for you. If you don't have a clue what this post is about, you probably don't need to waste your time reading any further. The attached video shows what the button will look like if you don't screw anything up.
Step 1.
Open the file: /plugins/tiny_mce/themes/advanced/skins/default/dialog.css
Find this line:
a.browse span {display:block; width:20px; height:18px; background:url(../../img/icons.gif) -860px 0; border:1px solid #FFF; margin-left:1px;}
Comment it out as shown below:
/*a.browse span {display:block; width:20px; height:18px; background:url(../../img/icons.gif) -860px 0; border:1px solid #FFF; margin-left:1px;}*/
On a new line, directly below the one you just commented out, add the code below
a.browse span {
background: url("img/browse.gif") no-repeat scroll 0 0 transparent;
display: block;
height: 18px;
margin-left: 3px;
width: 46px;
}
Step 2.
Upload the attached image, browse.gif to: /plugins/tiny_mce/themes/advanced/skins/default/img/
Step 3.
Delete all files in your sites cache_public directory. You may also have to clear your browsers cache.
DONE
Once you verify that this is working, you can delete the commented out line of css if you want to,