SOME function doesn't work

[sepwolves]

IE I want to Select the previous tab with "W", Select the next tab with "E"
but after I set it up in the key binding, it wouldn't work.
I just wonder why, and how could I solve the problem.
Other function is ok. I.E. "ar' will refresh all tabs, etc.

[sepwolves]

It seems that the problem is due to the Electrolysis project on firefox. When I turn of Multi-Process Fennec tracking, it work again.
But anybody could tell me why？