Rated 4 out of 5 stars
Once upon a time, Tbird provided TABS to switch between folder sets. I was sad to see that functionality go.
Arrow toggling shaves some time off doing it via dropdown menu, but configurable TABS means you get to the desired folder set with a single click.
Please consider replacing the arrows with tabs. Options which should be included are the ability to select which folder views appear as tabs on the bar and selectable order of their appearance (i.e., unread on first tab, all on second tab, etc.).
Also, for the KB warriors, you could add hotkeys to jump directly to desired folder views.
Thanks for your efforts.