LeechBlock is not compatible with Firefox 57+. For an explanation and information on a new version compatible with WebExtensions, go to: http://www.proginosko.com/leechblock/faq/compatible-with-firefox-57/
LeechBlock is a simple free productivity tool designed to block those time-wasting sites that can suck the life out of your working day. (You know: the ones that rhyme with "Blue Cube", "Space Hook", "Sticky Media", "Quitter", and the like.) All you need to do is specify which sites to block and when to block them.
You can specify up to six sets of sites to block, with different times and days for each set. You can block sites within fixed time periods (e.g., between 9am and 5pm), after a time limit (e.g., 10 minutes in every hour), or with a combination of time periods and time limit (e.g., 10 minutes in every hour between 9am and 5pm). You can also set a password for access to the extension options, just to slow you down in moments of weakness!
The sites to block can be specified using wildcards (e.g., *.somesite.com) and exceptions (e.g., +allowme.somesite.com).
LeechBlock also keeps track of the total amount of time you have spent browsing the sites in each block set.
For usage examples, go to: http://www.proginosko.com/leechblock/examples/
For answers to frequently asked questions, go to: http://www.proginosko.com/leechblock/faq/
For community support, go to: https://www.tapatalk.com/groups/leechblock/