Mozilla Firefox VS Internet Explorer?

I've used IE my entire life, now I'm wondering if it's time to install Mozilla Firefox on my Windows?
If I have both installed, my computer will be slowed down just a bit, right? It's already pretty slow.
Update: Can you explain WHY Firefox is better? Pros and cons?
Update 2: Alright, new question.
Firefox VS Chrome?
Update 3: Okay guys, at this very moment I am using Mozilla Firefox...
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