Grönsíir said:
Eh, found an extension called blocksite. It get's the job done although it's too easy for me to unblock the sites. But at least it reminds me I'm trying to get productive.
The best way (I've found) to avoid repeat visiting sites the moment you get bored is just by brute-force training yourself not to do it. Back when I had my dissertation I just publically said "I'm not using taleworlds or Facebook anymore" and I didn't need to actually block them. In fact after the first couple of days the reflex of clicking on Facebook or taleworlds was gone, and when I got bored I would just plough through it (or play video games for a little bit).
I tried using an app sometime before this but when I'm relying on technology to curb my short attention span, it's a lot easier to act like the responsibility isn't on me and so I just end up browsing other sites.