How can I contribute?

Go to the bug tracker (look at my sig), and search for something that might interest you.
Try to fix it or at least provide more info in the bug report (for example if a bug is missing some info and you can reproduce it, then explain it)
There are tons of work to do.
Testing the latest code, checking with different OS and browsers...

Just pick up whatever you want and ask for help if you get lost.