Xfailed tests due to new found issues

Sry for the confusing name of the branch, but initial I wanted to unxfail due to bug 842580 being fixed, but it got reopened.
Also there are two new bugs, cause a lot of problems in mk developers hub:
https://bugzilla.mozilla.org/show_bug.cgi?id=844052
https://bugzilla.mozilla.org/show_bug.cgi?id=844070