What steps will reproduce the problem?
1. Use Hyphenator.js as directed, but on XSLT output
2. Open in Firefox
3. Hyphenator silently fails

What is the expected output? What do you see instead?

It looks as if it posts a DOMContentLoaded event that never happens. I
tried substituting 'load' but apparently that never gets fired either.

What version of the product are you using? On what operating system?

I tried r590 but this goes back to ~r144.

Please provide any additional information below.

I'm not sure if this is related but I also have to manually load the
patterns/??.js, because that doesn't seem to happen automatically either.

This is a known bug in Firefox:
https://bugzilla.mozilla.org/show_bug.cgi?id=325891 and
https://bugzilla.mozilla.org/show_bug.cgi?id=391177 .

I work around the issue by manually loading patterns/??.js and executing
Hyphenator.hyphenateDocument() near the end of the document (in r144, I
can't get r590 to work at all). It occurs to me that some explicit method
of making sure everything gets run synchronously would make sense. I tried
tinkering with it, but it's a bit hairy and that is kind of an
architectural decision.