If you want to block posts on tumblr, here's advice from The Final Problem on how to do that. This is for tumblr tags.
Here's also some clever ways to help other tumblr users from The Norwood Builder... who is using really large warning images to indicate SPOILERS INSIDE and to keep you from being accidentally spoiled on tumblr.
Thanks to them both for their help and advice!
If you happen to be having problems working because of Twitter, or any other website, here's two helpful programs for your browsers.
This helps if you're trying to write -- or to avoid Twitter or FB -- or maybe you're hooked on fan vids or even tumblr.
I used to have LeechBlock [which I miss desperately!] but I haven't been able to properly reinstall Firefox on my PC. So now I use StayFocusd with Chrome. It is not as sophisticated, alas, as lovely LeechBlock was.