Bug 851349 - Disable browser_inspector_bug_831693_searchbox_panel_navigation.js for too many intermittent failures

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extra : rebase_source : dfc972c73c4c7e3a11e2695039b687048b478049
Bug 893714 - Disable test_cpows.xul on OS X for too many intermittent assertions, whilst the fix is finished

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extra : rebase_source : d3ad44b025610f5b1ec91f662eb9cbf5ba613a7d