I love the design of momentum itself, it’s a well done add. I really enjoy having such beautiful pictures in the background and it has such a clean look, which probably is the main factor for me to use this add on.
The only down side being that the add on doesn’t support Firefox iOS, please consider bringing this to Firefox iOS usages.

fantastic

Eats 30% of CPU when opened tab left in incognito window (after selecting name and "work offline")

I don't have the time to guess how this thing works. No instructions - not even on its web page.

Good.