To use this with the current Filezilla3 client you need to copy the tango folder into your Filezilla folder, then make a new folder named 16x16 inside the tango folder. Move all the icons into that 16x16 folder, then create a new file named theme.xml alongside the 16x16 folder and put the following into it....
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<FileZilla3>
<Theme>
<Name>Tango</Name>
<Subdir>tango</Subdir>
<Author>~sumowski</Author>
<Mail>sumowski.deviantart.com</Mail>
<size>16x16</size>
</Theme>
</FileZilla3>
This will let you select the Tango theme in the settings dialog.