Enable highlight of filter option that has focus (not sure why this was disabled).
Improve the focus system used with the explorer/editor filters so that the first option is given focus on opening a filter. For example, now when you click Search you can immediately start typing whereas before you had to click on the text field first. Although not perfect, it also makes navigating the filters using just the keyboard (ie. TAB key) that bit easier.
add @Override.
refactoring: use diamond inference; use final; isEmpty instead of "".
escape key can be used to hide/close filter popup panel.