Tools nathuwa lesiyenma puluwan Windows wala host file eka edit kalanam.
Open the hosts file under C:\Windows\System32\drivers\etc then add
# 127.0.0.1 siteYouWantToBlock.com
To the end of the file.
This will redirect the site you want to block back to your own PC. Therefore all programs and browsers will not be able to connect to that site afterwards.