U.S. Stocks Set for Slightly Firmer Open  NEW YORK (Reuters) - U.S. stocks were set to move slightly  higher at the open on Friday with a \$1 billion share buyback at  Texas Instruments Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=TXN.N target=/stocks/quickinfo/fullquote"&gt;TXN.N&lt;/A&gt; supporting technology stocks,  although rising oil prices could limit gains.