Closing the issue as this is now working ok.
Everything is okay now, don't know why but it is ;)
Could you please provide a screenshot of how it looks as it is supposed to and how it looks in pekwm.
Can't really see how the scrollbar inside of firefox has anything to do with pekwm, apart from the rare chance of pekwm resizing the window and sending broken size information.
pekwm --info output as well please. :)