Ctrl+Tab between threads
Hold Ctrl and press Tab to step through your threads, most recent first, the way Alt+Tab steps through windows. Let go and you are there. A quick tap flips between the last two.
Ctrl+W settles the thread you are in and takes you to the last one you visited that is still open. It leaves a working thread alone and never closes the window.
Shift goes backwards, Esc cancels, and the list takes clicks too. Drafts are in it, and it survives a restart.
Your browser keeps Ctrl+Tab for its own tabs, so here the buttons press the keys.