There is an Add-on available for Mozila Firefox named “BlockSite” which helps users to block websites of their choices and password protect the settings to stop unauthorized changes. So just follow the simple process written below to block sites in Firefox.

Block Web Sites in Firefox

Step 1

Add BlockSite extension to Firefox

• Click on Get Add-ons.
• Type “blocksite” in search field.
• Click on “Add to Firefox” button to install.

Step 2

Restart Firefox and navigate to “Tools” menu and select “Add-ons”

Step-3

Select “Blocksite” from extensions list and click “Options”

Step-4

• On following window click on “Add” button to add URLs that you want to block.
• Check the enable authentication check box and enter a password to protect from anyone to make changes in this block list.