Bug 1055977 part 1: Use !important (and 'initial') in full-screen-override.css, to more thoroughly prevent ancestors of a fullscreen element from creating stacking contexts. r=dbaron
Bug 1055977 part 2: Add mochitest to verify that ancestors of a fullscreen element are fixed at the initial values of any properties that can create stacking contexts. r=cpearce

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rename : content/html/content/test/file_fullscreen-hidden.html => content/html/content/test/file_fullscreen-ancestor-stacking-context.html