That's a terrible list of why your system is slower.
Lots of Firefox extensions? Since when does Firefox have anything to do with the performance of the underlying system? Firefox may start up slower or run slower, sure, but that's not going to affect your system performance.
OS X is
awesome... but the average person that uses them is definitely not. I think I'll write an article "17 reasons why Windows runs slower than it should." Starting with reason #1, "You have too many achievements in
TF2."