Bug 918782 - [Australis] move functional customize mode styles to browser/base, r=mconley

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extra : rebase_source : d0ac2b415d1c7ab1c02219e954e66d6819347baf
Bug 938995 - Australis' customize mode sometimes doesn't close, restore defaults stays enabled after clicking, r=jaws
Bug 935628 - Remove BrowserToolbarBackground class (r=sriram)