Bug 857883, don't assert about readyState when not needed, r=bz

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extra : rebase_source : 1dc9dc6bae5907cac3f2b8b1c31d79e7bcbb68f2
Bug 862309, remove useless warning about missing presshell, r=mats

--HG--
extra : rebase_source : 5f77555a3a24bc27cb3ce4422d6f06e1d4b97ab3
Bug 848253, release memory sooner when mutating session history, r=jlebar

--HG--
extra : rebase_source : 12bebdec8d72d55bbda9b12d2ad2ceeab7928a4a
Bug 848535, simplify js object holding in XHR and FileReader, r=mccr8

--HG--
extra : rebase_source : d10c2315bf3eafb0e3ef7f4199c1439e96c47da3
Bug 866915, update XHR.send to follow the spec, r=sicking

--HG--
extra : rebase_source : ee7ce01fa3a71db5327e42f40a725db99efbe345