OK, well, I discovered that the separate <script...> I was using doesn't work in Safari, so I had to switch things up so that it's similar to the method used in the original reply to this question:

<input type='text' id='date' name='date' style='text-align: center;' size='10' maxlength='10' value='' onClick='Calendar.setup({align : "br", inputField : "date", ifFormat : "%Y-%m-%d", weekNumbers : false, step : 1}); var evt = document.createEvent("MouseEvents"); evt.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null); this.dispatchEvent(evt);' readonly>