Firefox doesn't have a way to throttle the download speed.
You will have to use an external download manager to get extra features like that.

• http://plugindoc.mozdev.org/windows4.html

You can use the FlashGot extension to integrate an external Download Manager in Firefox.

• FlashGot: https://addons.mozilla.org/firefox/addon/flashgot/

Hey I am quite novice related to computers.. Could anyone please tell me the exact procedure of how I can limit the download speed. I saw the solution posted to my question but I was unable to execute what was asked. Can someone tell step by step procedure. I am sure this will help a lot of people like me.

You will first have to install a download manager that supports this feature to throttle downloads to a specific speed and verify that FlashGot supports this manager.

See http://flashgot.net/