Blocksite is a Mozilla Firefox add-on that allows you to block access to any websites that you designate. https://www.blocksite.live/

1. How to Use BlockSite to Unblock Websites
Blocksite is a Mozilla Firefox add-on that allows you to block
access to any websites that you designate. While this is beneficial
in a business setting to prevent employees from accessing specific
types of websites during working hours, it is also feasible to
accidentally block a website you want to visit later. If you get an
error notice saying the site is on the BlockSite blacklist and hasn’t
been loaded, go to the BlockSite settings and remove it.
· Click the orange Firefox button in the top left corner of the
window to open the Firefox browser.
· Then select “Add-ons” from the drop-down menu that appears.
· To see a list of all installed browser extensions, go to the left side
of the screen and choose “Extensions.”
· Click the “Options” button next to BlockSite, and then on the list
of locations presented, click the URL of the website you want to
unblock.
· To unblock the websites you’ve chosen, click the “Remove”
button.
· To complete the process, click “OK” and then shut the Add-ons
Manager tab.

2. Read More: Blocksite Extension