Bug 972140 - fix tabbrowser-tabs min-height for Australis so it doesn't get squashed when the non-abs-pos bits have 0 width, r=mconley

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extra : rebase_source : a233b0be8a28a3fbb9cd49608655be9e7495be8f
Bug 978251 - nullcheck target in Australis' panel click detection code, r=jaws

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extra : rebase_source : 4bd6b3121fe298961f0354054508debf75d62e86