This is something I have been putting up with forever. Firefox on OS X is just horrible. It is either using 99% CPU or else it is just running slow all together.
Yes I do use plugins however disabling them really doesn’t help. Even if it did, what would be the point? The only reason I am still using Firefox is because of the plugins.
I was happy when Mozilla released Firefox 3.5 beta, hoping that would fix the problem but no it didn’t.
I’m really hoping that either Safari or Chrome allows for plugins to be created in the future.