To block web pages on Linux Mint, there is a simple tool in your Control Center. Go to Menu > Control Center > System > Domain Blocker and you will be asked for your password. A plain window with just a few buttons will appear afterwards.
To add web pages to the blocking list, click on Add and type in the (un-)desired page. It may occur that you have to enter it two times, one with www. and one without www..
To adopt the changes restart your browser and the entered web page should no longer be available.