Any good freeware hard disk defragers?
You can cruise through this page and see what you like:
I use O&O Defrag Professional, but they have a freeware version on there as well.
Any good Mozilla freeware security software?
Not sure what you are asking... Stuff by Mozilla, stuff for Mozilla, what?
Firefox is fairly secure, but all my security stuff is by different people... not that what I call security is really security. I'm talking about stuff to protect my system (firewall, A/V, A/spy, stuff like that).
Care to expound a bit?