The Media Browser dialog uses the Thumbnails view by default. This may be inconvenient in some cases.
There are two ways of dealing with this problem:
MediaListviewItem control has the following location:
\sitecore\shell\Applications\Media\MediaShop\MediaListviewItem.xml.
In this control you can modify the width and height attributes of the thumbnails as well as other layout settings.
Below is an example of the modified control source.
<?xml version="1.0" encoding="utf-8" ?>
<control xmlns:def="Definition" xmlns="http://schemas.sitecore.net/Visual-Studio-Intellisense">
<MediaListviewItem>
<Border ID="$ControlID" Class="scListviewItemThumbnails" Width="150" Height="60" ToolTip="$Header">
<GridPanel Columns="2" Width="100%">
<Border GridPanel.VAlign="top" GridPanel.Width="25%">
<ThemedImage Src="$Image" Width="50" Height="50" Margin="3 3 3 3" ToolTip="$Header"/>
</Border>
<Border Foreground="#999999" Padding="3 3 3 3" Align="left" GridPanel.Width="75%">
<Border Foreground="black" Style="font-weight:bold">
<Literal Text="$Header"/>
</Border>
</Border>
</GridPanel>
</Border>
</MediaListviewItem>
</control>
As a result, the thumbnail size is decreased.