This is what I've experienced with 3.8.1.
Very bad layout of images and semi system-crash.
Below I've linked an example were no problems there are with konqueror while with firefox I've a very bad layout (sort of negative) and cpu usage jump over 50% with a semi-freeze of my system (try to open an app while this pdf document is open with firefox to notice that). Both konq and firfx opens the document with acrored 4.0, the only difference is that in konqueror is open out of the browser while in frfx is embedded, but if you select 'open in new tab' in konq. the pdf will be opened inside the browser without problems.
example:
http://www.barco.com/projection_syst...s+_win2004.pdf

someone can confirm this?