On the feedback page, I had several people asking to have a better way to access the namespace filter menu. I'm not the only one to have that feeling.
I suggest users to use the search bar to type a filter name, which is apparently a feature not visible enough. T178539 adds more prominence to the Namespaces and Tags menus. But in addition, to give more prominence to the searching, let's tweak the default message in the search bar:
Filter recent changes (browse or start typing)
[please change to]
Filter changes (use menu or search for filter name)