As reported by Mike, the Math-o-mir had a bug on dual-monitor systems: pop-up menus were restricted to primary screen only. I solved this today (it was easy).
Today I also added support for ‘home’ and ‘end’ keyboard keys. The first instantly moves the cursor to the beginning of an equation/line, while the other moves it to the end. Not sure if I am happy with this implementation.
I am thinking now to implement a way to move cursor between two nearby equations by using keyboard arrow keys, without any need to touch the mouse. As it is now, the arrow keys moved cursor inside single equation only.