XML Editing in Firefox
XML is the language of the Web. Whether you build Flash applications, code Ajax frontends or simply want to import data from a Mysql-based application, XML is your friend. The XML support in Safari is.. well let's say "basic", so most Webdesigners and Developers used Firefox for XML-Related tasks anyway.
Now the new Firefox 1.5 offers a bunch of new and hot XML Editing & validation functions, IBM has a good overview of those.