Blame Apple and Mozilla, too, then. They all agreed to remove it.
They all agreed because XSLT is extremely unpopular and worse than JS in every way. Performance/bloat? Worse. Security? MUCH worse. Language design? Unimaginably worse.
EDIT: I wrote thousands of lines of XSLT circa 2005. I'm grateful that I'll never do that again.
> Security? MUCH worse.
Comparing single-purpose declarative language that is not even really turing-complete with all the ugly hacks needed to make DOM/JS reasonably secure does not make any sense.
Exactly what you can abuse in XSLT (without non-standard extensions) in order to do anything security relevant? (DoS by infinite recursion or memory exhaustion does not count, you can do the same in JS...)
While that is often neat solution, do not do that by simply XORing the numbers with constant. Use a block cipher in ECB mode (If you want the ID to be short then something like NSA's Speck comes handy here as it can be instantiated with 32 or 48 bit block).
And do not even think about using RC4 for that (I've seen that multiple times), because that is completely equivalent to XORing with constant.