I use Firefox on my Mac and have hundreds of website passwords saved in its password store. I don't even remember my passwords half the time for the various sites that I use. How can I sync the usernames/passwords between the two devices? I'd also like to be able to sync my bookmarks if possible. I use Firefox Sync to keep my various computers in sync, but of course this will not work with the iPad.
For passwords, I highly recommend 1Password.
It will enter the passwords into Safari for iPad and it will sync your passwords with your Mac (if you setup the sync), and then you can search for what you need on the iPad.
You can synchronize your Firefox bookmarks with your iPad using iTunes:
Firefox Home is intended to sync as much data from Mac Firefox to the iPad as possible. If that's not enough, you'll need a desktop program to get firefox syncing data to Safari and then through MobileMe or USB to the iPad.
I'd go with 1Password for passwords and Firefox Home for the rest.
If you create a Firefox account, you can sync your bookmarks and passwords across all devices. I created an account so I could access all my bookmarks and password across an android, iOS, windows, and Mac devices. It works brilliantly to sync everything and back up your information.