MP3 Diags
Click on in the main window or in the tag editor to open this window.
Here are the settings that don't belong anywere else.
Among other things, you can play with the icon size.
The full name of the normalization program should be enclosed in double quotes if it contains spaces, e.g. "C:\Program Files\mp3gain\mp3gain.exe". If any parameters of the normalizer have to contain spaces, they must be enclosed in double quotes.
Also, you can choose here to display "close" buttons in the upper-right corner of several windows, which allows you to close those windows easier with the mouse. This is a usually a Gnome 3 issue, but it depends on how Gnome 3 has been configured. The default for the this setting is not always correct. The idea is to show these buttons if Gnome 3 is installed. One issue is that this is not always the right thing to do, for several reasons. Another issue is that the detection of Gnome 3 isn't quite right. If anybody has better ideas, please let me know.