For bugs in Firefox Desktop, the Mozilla Foundation's web browser. For Firefox user interface issues in menus, developer tools, bookmarks, location bar, and preferences. Many Firefox bugs will either be filed here or in the Core product. (more info)
I have reddit open in a pinned tab.
In non-e10s if I click on a story that's not on reddit.com, the link is opened in a new tab.
In e10s if I click on the same link, it's opened in my pinned tab instead.