Bug 853334 - Fix testaddons on fennec

So I ended fixing require test, but also others test addons.
The common error is that require(panel) should be avoided in favor of fennec-compatible modules.
Otherwise I disabled the windows test on fennec in private-browsing addon,
as it fails a lot and I'm not sure it is really usefull as we only have a single window on fennec?
https://bugzilla.mozilla.org/show_bug.cgi?id=853334