making mozilla's xml to behave in a non-standard way

hi, this is a strange question I know, but I hope to get some responses:

        I have a web application that I can't modify. it outputs an xml to
the browser with newlines and spaces at the beginning of the xml.

now the question. How can I modify this behaviour of mozilla? how can it
be more tolerant to this malformed xml?

If you have any hints on where to look at the code or if it's possible
to write an extension (mozilla-firefox) please let me know.

thanks.

ciao,
Marco