Since I tend to get distracted easily (by multiple unrelated websites) when I'm browsing the Web, I want to find a way to stop some websites from being opened in a new tab when other specific websites are open.
You can use this extension: Controlled multi-tab browsing
Set maximum tabs that can be opened and restrict yourself from opening tabs more than the set limit. The multi-tabbed browsing is good. But when you find yourself just keep opening too many tabs and using very few of those, it is not good.
The habit of opening too many tabs may hamper your system performance. Also, you might waste your time just traversing in between the opened tabs or managing those using some fancy extension and often learning nothing. So, I suggest you to keep some well-judged limit on the number of tabs and to adhere use "Read and Discard" strategy.
Try this extension, set your tab limit and you will really find yourself learning more by actually using/reading the webpages rather than just managing and traversing the opened tabs.