Depends on your anti-virus. Most of them have the option to block a given site (look in the "Settings" menu), but you can also block it with your firewall.

Firefox though is just a browser: it doesn't have the ability to block sites.

What I suggest you do is to download the free version of Malwarebytes from http://www.malwarebytes.org/products/malwarebytes_free and then run a full system scan.

You also need to update your plugins because several of those are out of date which potentially exposes your system to attacks of the kind you're experiencing at the moment. You can check which ones you need to update by visiting the Plugins Check page.

Greetings.

1. Use this:

https://addons.mozilla.org/en-US/firefox/addon/blocksite/

2. Or use http://noscript.net/

3. Or use host file in win XP.

type in windows explorer

%windir%\system32\drivers\etc\hosts

open with notepad

127.0.0.1 localhost

127.0.0.1 insert.website.name.here like example:

127.0.0.1 www.malwarewebsite.com

Save and exit.

Cheers

RaZoR