[LEFT]I have been using IE for a long time and have just migrated to Mozilla Firefox. I am amazed at the speed it opens up pages as well as its features. But I have to go through a lot of articles offline, which was possible under IE simply by activating the "view offline" options. I want the same type of options here. How do i do so. Do I need to download any extensions for such a facility and if so please let me know the name.[/LEFT]

Welcome to TechSpot

You don't need any special settings. Under Tools/Options/Download you have the setting where your downloads go. This ia also the default for offline-viewing.
If you like or need a webpage, just click on (top left) Files, select 'Save Page As ...', give it a differenet name if you want and/or change/confirm the directory. That is all.

When you then go to that directory and click on the file with .htm or .html extension, you see the whole thing offline. Or open the browser, and select Open Location or Open File.