Bug 964104 - fix icons moving when pressing down on Australis for Linux, r=jaws

--HG--
extra : rebase_source : 6050239e8964d2040f6fcaf428e88201fe0ac6da
Bug 969376 - correctly size Australis' menu button, make it hug right border on Windows and Linux, r=jaws

--HG--
rename : browser/base/content/test/general/browser_backButtonFitts.js => browser/base/content/test/general/browser_menuButtonFitts.js
extra : rebase_source : 340dcab974bf49f1e3abfc18e0e7217bb5803411