S3 Browser automatically applies content type for files you are uploading to Amazon S3. And you can control which Content Type will be applied for a specific file type. By default all Content Types are taken from the system.

To view and edit Content Types click Tools -> Content Types. You will see the following dialog:

S3 Browser content types (mime types) viewer and editor.

Add, Edit and Delete buttons can be used to add, edit and delete custom content types. Custom Content Types has higher priority than system Content Types, so if you want to override system Content Type, you may just add custom Content Type and specify any string you want.