When I looked at support for XPointer in Firefox I ended up using quite some time trying to get my blog pages (through blogger.com) to become clean and valid XHTML, as the template states. That was by far no easy, and the three main problem areas was:
* The template with markup
* The code thats included automatically by blogger.com (the navigation bar)
* The markup generated by the custom layout tags
* The markup used in the posts
I googled for some help but didn't find much and most of my findings were either for the old version of blogger.com or regrets that it still wasn't valid XHTML we are in the year 2007, more than 7 years after the first recommendation for XHTML.