The alt combinations (other than alt+esc to activate) don't work for me. I thought it was because they were captured by the browser or something, but it also does nothing when clicking on them.

And isn't alt+space a global combo in most major OSes? (Window operations in Windows and most Linux distros, and some system dialog in macOS if I'm not mistaken, though that might have been cmd+space.) I use it frequently (mostly to minimize windows but also for other things), and while most people may not do that, I think this extension targets exactly the audience that would. Seems like an odd choice.