Feedburner provides custom RSS feeds that allow web site publishers to collect statistics on RSS readership and enhance their feeds with photos, affiliate links and eventually ads. While it publishes feeds for thousands of web sites, Feedburner’s data represents a small slice of a complex market that has become even more crowded in recent months. Its stats from the first week of January found 719 different RSS clients, compared to 409 in September. That increase is likely tied to growing integration of RSS in applications and web sites, rather than desktop readers.

Firefox has been downloaded more than 14 million times since Version 1.0 was launched Nov. 9 with improved handling of RSS. While most comparisons in the renewed browser wars have focused on security or usability, the Feedburner data suggests that Firefox’ RSS features are being used by a significant percentage of its users.

Internet Explorer does not yet have a native newsreader function. In an interview with Gizmodo, Microsoft Chairman Bill Gates said he uses RSS and hinted at Microsoft initiatives to address the growth of blogging and RSS. “I have the add-on to Outlook that lets me see (RSS feeds),” Gates said. “I think blogging is super-important and we’ve got to do a lot more software.”