I have a raspberry 2 (with raspbian), I installed Iceweasel and I added the addons iMacros. I created a script in js, is really very slow, however, is only used 25% of CPU and less than 50% of ram. Why it can not use all the resources? and complete the task in less time?
You are processing a single task on your raspberry pi.
The raspberry has a quad core processor (product page).
Because a single task can only run on one core the same time, only 25% of the cores are fully used.