bug 936198 - update small Yahoo! icon, including on MetroFx, r+a=gavin

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extra : rebase_source : 8ab120eb3c6b49fe182255d11b593792d76df6ee
Bug 936198 - Updated Yahoo Logo for Metro, r=mbrubeck, a=gavin

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extra : rebase_source : 31bdeaf55be9b886dec1b7f4ff5ba42b00375742