Steps to reproduce the issue

Just load administrator in mobile Firefox browser(Android). When pushing the Hamburgermenubutton, you are redirected to the homepage on the frontend.

Expected result

When pushing the Hamburgermenubutton we should see the administrators mainmenu as a vertical mobile menu.

Actual result

When pushing the Hamburgermenubutton, you are now redirected to the homepage on the frontend.

System information (as much as possible)

Latest Firefox mobile browser (Android)

Additional comments

This is very easy to fix:

Just add the attribute href with the "#" value: href="#" to the <a....> on line 154 of index.php of the isis template. So line 154 become:
<a href="#" class="btn btn-navbar collapsed" data-toggle="collapse" data-target=".nav-collapse">