How to script XPI installation for Mozilla 1.7.10

Hi,

we are currently trying to customize the RedHat distribution, that
comes with a Mozilla 1.7.10. Unfortunately, the german language pack is
not included.

As for that, we want to make a rpm-package that includes the German
language pack "mozilla-1.7.10.de-AT.langpack.xpi".

Is there a command line option or any other way to script it in a clean
way into the spec file?

However, all alternatives such as taking the prepackaged binary from
Mozilla.org or making a diff before and after a browser installation do
have significant drawbacks.

Searching the forum, I saw a similiar question, but there were no
answers posted. I would really appreciate someone to help me out
here...

Tanks in advance,
-Ron