How to block Websites in Mozilla Firefox

Open Firefox, click "Tools" then "Add-ons." Click "Get Add-ons" and then "Browse All Add-ons." Type "blocksite" in the search bar after the Mozilla Firefox add-ons website opens and hit "Enter."

Click the "Add to Firefox" button next to the entry for BlockSite. Allow the add-on to load (usually less than 5 seconds), then click the "Install Now" button. Restart Firefox when prompted.

Go to "Tools," then "Add-ons," then click the BlockSite "Preferences" button after Firefox restarts. Make sure the "Blacklist" radio button is ticked, as well as "Enable BlockSite," "Enable warning messages," and "Enable link removal."

Check "Enable authentication," then enter a password if you would like to keep other users from deleting blocked websites or changing the settings in BlockSite without your permission.

Click the "Add" button, enter the URL of the website you would like to block, then click "OK." Repeat to add more sites, or click the "Clear" button to delete the list. Once the list of blocked sites is complete, click "OK" and restart Firefox.