browser error when using xpath2.0 functions

Hi,

I am using XPath 2.0 functions and its new vocabulary like except, tokenize, if then else and other stuff. i am also using some user defined functinos which i am calling in my style sheet. I am trying to run this xsl in Mozilla firefox but its throwing off an error saying 

"Unknown xpath extension function error" 

its not recognising these things even though i have included the namespace of xpath2.0 obtained from www.w3c.org but still its throwing an error.

I have seen other xslt programs which are using it but have not been able to resolve how to execute my stylesheet. I would like to know which browser version to use I would like to use MOZILLA and avoid these errors. please suggest an alternative.

with regards,
Prasad
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