I hope this interests someone...
I just updated my Kindle Touch to 5.1.0 and I found out that orientation now doesn't works with browser and WAF applications.
Playing around, I managed to make the GUI launcher orientation script to work even in the home screen. I changed the value of this entry in appreg.db to URL (instead of U):
Anyway, creating a similar entry for the browser or any of the WAF doesn't work.