Bug 969376 - correctly size Australis' menu button, make it hug right border on Windows and Linux, r=jaws

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rename : browser/base/content/test/general/browser_backButtonFitts.js => browser/base/content/test/general/browser_menuButtonFitts.js
Bug 969376 - fix all the tests for Australis panel to not go orange because of promises and weirdness, r=jaws