@fengwang Methinks this would not be so good on the readability and usability fronts, as scanning back and forth over large horizontal "distance" is more fatiguing for the eyes. Hence, I suspect the logic behind the present presentation. As for changing it, sorry, I've not a clue.
Shrink that browser window and utilize the space for something useful. Like running an IRC client, your favorite editor, etc.? Are these monitors all connected to the same box or different machines? If same, then maybe consider running one or more in "Portrait Orientation". Dandy set up for editing long files and scanning long running threads or categories with lots of active posts:
If the devs that be do change this then I pray that it will become a config knob rather than the default.
Just a few related thoughts. Sorry I cannot offer a quick fix to scratch yer' itch.
Take care and have a groovy day.