DOCBOOK-APPS: undefined entity ò in Mozilla

If I try to load one of my DocBook XML 4.2 documents (no XSL stylesheet
referenced in the XML file) in Mozilla 1.0.1 I get the following error
message:

XML Parsing Error: undefined entity
...
Line Number 4525, Column 19:            
        <emphasis>&ograve;</emphasis></para>
------------------^

Is this a known bug/behaviour in Mozilla?

Michael
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