Yea it hooks into the PDF core that Safari uses. When I meant issues I was mainly referring to cosmetic. For instance you need to goto File-Save page in order to save the pdf (Should also be able to right click).
Author is working on this and more features. Regardless I'm happy ... PDF viewing was the only thing I hated about FF2.
Bummer though first pdf I viewed displayed HUGE and I had to - a bunch of times to shrink it down. Wish there were preferences where I could specify to shrink to the width of firefox.