I'm getting the same problem, and guess what, it started to appear out of the blue on a production applications that had been happily running for a number of years after Richfaces 3.3.0.GA was introduced.
So far I'm having no luck in fixing the mysterious error that seems to be isolated to Firefox 2 and just about identical to the original report in this thread.
Will report back on this issue once I find a fix.
As posted above:
<f:view contentType="text/html"/>
will fix it. This error is caused because firefox refuses to display badly formed xhml strict documents. This means that if you have something like:
#{user.name}
and the user has a ampersand in their name your page will die. The good thing about this error is that firefox tells you exactly where on the page it is happening, so you can look at the generated html and fixgure out where in your page the problem is occuring.
According to XML Parsing Error: mismatched tag Firefox seems to be buggy:
The parsing error is caused by a href with a staring slash. Removing this slash firefox can parse the site.
Just to note that my error went away after I added
<f:view contentType="text/html"/>
just within the respective body tags in my templates.
Thanks Staurt.