Are there considerable browser-specific differences in xsl transformation, or am I being overly cautious?I've been using browser-side XSLT processing for three years. Although I had initial share of problems with IE5 and some releases of IE6 (finally forcing me to perform server-side transformations for IE5), IE6/7 and Firefox behave almost identically as long as your XSLT is valid. Firefox is a bit more relaxed in error handling, so it might survive an invalid stylesheet and ignore the error. Handling XML/XSLT errors on IE is a nightmare: if the XSLT transformation fails, it's almost impossible to reload the document without closing the browser (obviously IE has some serious caching problems with XML documents). To test new XSLT transformations, I usually force server-side transformations and receive good error messages from server's MSXML.
Opera is a different story. It didn't support XSLT until pretty recently and even then the document() function was broken. I have simply decided not to offer XML data to Opera visitors (they are a minority anyway) and Safari is not widespread enough in my customer base to notice.