I have already mentioned how to block any website in any web browser but if you want to block certain website only in Mozilla Firefox then follow the steps below.
To block any website in Firefox you don’t have to do much work, just need to download a plug-in and rest it will take care of it.
Just install the plug-in called FoxFilter which has the ability to control the content a user is surfing and even block certain sites selected by you. It runs on Firefox whether you use it in Mac, Linux or Windows.
You can easily update the settings of this plug-in once you have installed it and it also Include password recovery feature.