LeechBlockList maintains a list of time-wasting sites to be blocked by the Firefox plugin LeechBlock. Here's how to get blocking right away:
1.
Install the LeechBlock plugin for Firefox.

2.
Select LeechBlock > Options from Firefox's Tools menu.

3.
Enter http://leechblocklist.appspot.com/list in the Load from URL field.

Bonus:
Maintain your own list of LeechBlock rules with a Google Account.

With LeechBlockList, you can access your LeechBlock rules from any computer. We also maintain a list of common rules, so you won't have to manually add rules for many of the time-wasting sites you undoubtedly visit.