hi guys
I asked about this trick in meetup in London.
Man said that there is no proximity sensor or capacitive button.
however it works only in WEB app.just to switch btw current page to the history.that's all.
To switch you have to tap on the right side of the n900 NEAR the screen and then slide to the left. it might work.try it
sorry for bad English.I'm trying to improve it)