Test details page bug fixed and xfailed test_user_can_go_back_from_setti...

This was intended from the beginning -> Visit Settings, click Apps, click Back, test that the current page is the homepage.
https://bugzilla.mozilla.org/show_bug.cgi?id=795185#c11
I wanted to change the test but it seems that this is not the normal behaviour so I reopened bug https://bugzilla.mozilla.org/show_bug.cgi?id=804759
and xfailed test