Firefox Slows down

In recent times, I observed firefox slow down significantly. It takes time to open and hangs for half a minute before we can use the browser. Is it due to usage of multiple add-ons that is causing this problem?

I've been using Safari browser for some time now. I believe it is the best among Safari / IE / Firefox / Chrome. Safari opens up quickly without much trouble and I never observed it struck up even after I open multiple tabs. However, one issue I've with Safari is the non-availability of add-ons.

This must be the key reason for Firefox slowing down.