Seam 2 uses enum types to associate file extensions with mimeTypes (in s:graphicImage for instance, and perhaps 1 or 2 more places) - see WhySgraphicImageCanNotShowBmp.
Enum types cannot be extended, so if we want to handle another mimeType, we must patch Seam 2.
Could Seam 3 use javax.activation.FileTypeMap instead (i.e. just call FileTypeMap.getDefaultFileTypeMap() ?). This would be better to provide new mimeTypes (i.e. see discovery sequence in MimetypesFileTypeMap)