We currently have inconsistent logic when setting up a file filter for `File` and `File[]` inputs. The `extensions` style is only supported for `File[]` inputs, not for `File`, see: https://github.com/scijava/scijava-ui-swing/blob/08fb795cd8bd8c119b1f6139592deab37f803503/src/main/java/org/scijava/ui/swing/widget/SwingFileWidget.java#L137 Actually, the file filter seems to work for drag-and-drop (in `FileHandler`): https://github.com/scijava/scijava-ui-swing/blob/08fb795cd8bd8c119b1f6139592deab37f803503/src/main/java/org/scijava/ui/swing/widget/SwingFileWidget.java#L357-L358 ... but not for the *Browse* button. Related `scijava-common` issue: https://github.com/scijava/scijava-common/issues/197