IE 10+, Chrome:<br />

<label>.xls,.xlsx files</label>

<input type="file" accept=".xls,.xlsx" />

<br />

<br />

IE 10+, Chrome, Firefox:<br />

<label>.xls,.xlsx files (using MIME-types)</label>

<input type="file" accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,application/vnd.ms-excel" />

​

<p>

    <b>Note:</b> Firefox (upto version 32 Nightly, at least) allows to choose files of any type by default, even if accept attribute is set, although it adds a custom filter list to the file-select dialog box. The user must manually apply the filter from the file-select dialog box.</p>

<p>(All tests were done on Windows versions of Firefox and Chrome, (and IE 10 :p))<p>