As a developer, I run Firefox all day long. Then I began to notice that Firefox would get progressively slower, to the point where it wouldn’t want to move anymore. So here is how you can diagnose and fix the problem to make Firefox faster:
1) open “Activity Monitor”
2) Notice how on mine Firefox is reaching 1GB of memory?
3) Close Firefox and whatever else you think is being a memory hog.
That’s it. It will be faster. I recommend doing this 2-3 times a day.