Hi,
Jonas Sicking wrote (29.12.2006 at mozilla.dev.tech.xslt):

We now have code checked in to support some parts of EXSLT
These functions will be supported in the upcoming Firefox 3
release (sorry, no chance of backporting to earlier releases)

exsl:node-set
exsl:object-type
regexp:test
regexp:match
regexp:replace
set:difference
set:distinct
set:intersection
set:distinct
set:has-same-node
set:leading
set:trailing
str:tokenize
str:concat
str:split
math:min
math:max
math:highest
math:lowest

The above functions should work in the current nightly builds. Please
test and report any problems.