How to change proxy in FireFox
save those proxies in a notepad file, name it as proxylist1.txt or any u want.
Enter the proxy and the port from the file u just saved (proxylist1.txt) and click on Use this proxy server for all protocols.
click on OK.
go to this site and check your new IP address
For best results, always use fresh proxies. Google for more proxies.
about the speeds: download speeds will depend upon the proxies.
Also check How To Open blocked Websites in Internet Explorer.