How to block site in Firefox?

How to block site in Firefox?

Step 1 

Surf to BlockSite's add-on page on the Firefox add-ons website or Click
here to Add directly 

Step 2

Click on "Continue to download." On the next page, click "Add to Firefox." You may optionally also contribute to the support and development of the add-on.
 
Step 3

Click "Install now" on the dialog box that opened up. Restart Firefox to complete the installation.
 
Step 4

Click on Firefox's "Tools" menu and choose "Add-ons." Highlight the BlockSite add-on.
 
Step 5

Click on "Options" to open BlockSite's settings. If you want to set a password to prevent future unauthorized modification of these settings, check "Enable authentication" and type a password. Future attempts to open "Options" will prompt for this password.
 
Step 6

Click on the "Add" button and type in the website address of the website to manually block. Repeat as desired. Hit "OK" when done. From now on, Firefox will not allow access to those websites.