middle mouse click displays linked content in current tab

[Thibaut Brandscheid]

Description: Ubuntu Wily Werewolf (development branch)
Release: 15.10
webbrowser-app: 0.23+15.10.20150729-0ubuntu2~gcc5.1

What you expected to happen:
I'm using the browser on the desktop. When middle mouse clicking on a link I expect the browser to open a new tab in the background and stay at the current page. This way it is possible to continue reading the current content and read the linked information later. All major browser implement the middle-mouse-click event as described.

What happened instead:
* middle-mouse-click on link.
* current tab (tab1) keeps focus, but displays the content of the clicked link (bug).
* a new tab is created (tab2).

* when clicking on the new created tab the focus switches to the new tab (tab2).
* the same content is displayed as in the previous tab (tab1).
* when switching back to tab1, the web page is displayed like it was before middle-mouse-clicking it (as is should have been the whole time).