Browser Extension: When in a pinned tab, external links open in a new tab
https://chrome.google.com/webstore/detail/sticky-pinned-tabs/mjlgfnggkljhiipiiogoengknkfocbkp
It's technically a Web Extension, but it doesn't work in Firefox yet. You can install it by loading the manifest.json from the page about:debugging
You can install the Chrome extension in Opera by using Download Chrome Extension