This window is opened from the main inventory window, when clicking the bottom gear icon and selecting Show filters.
It has check boxes which, when enabled, will included that type of item in the inventory display. To hide (for example) notecards from being shown, uncheck the Notecards checkbox.
To select all types of items, click the All button; to deselect all types, click the None button.
See this page for documentation on Firestorm 4.7.7 (48706) and earlier.