Packages provided by linux distributions usually prefer to depends on a shared library from another package rather than providing the same library in different packages (e.g. when there is a security problem the distribution only need to update 1 package; also save space on drive). Debian provides spidermonkey inside xulrunner packages that are already used by other packages. This is what I get on an Ubuntu 10.04: $ apt-cache rdepends xulrunner-1.9.1 xulrunner-1.9.1 Reverse Depends: zekr xulrunner-1.9.1-testsuite xulrunner-1.9.1-gnome-support xul-ext-flashgot |xul-ext-flashgot xul-ext-firecookie |xul-ext-firecookie xul-ext-firebug |xul-ext-firebug videolink python-hulahop |mozzemberek mozilla-nukeimage miro libgtk2-mozembed-perl libgtk-mozembed-ruby1.8 libgjs0 libgjs0 kazehakase-gecko galeon xulrunner-1.9.1-dev xulrunner-1.9.1-dbg $ apt-cache rdepends xulrunner-1.9.2 xulrunner-1.9.2 Reverse Depends: xulrunner-1.9.2-testsuite xulrunner-1.9.2-gnome-support xiphos tuxguitar prism mozzemberek moonlight-plugin-mozilla google-gadgets-xul gnome-web-photo fennec eclipse-rcp conkeror chmsee yelp xulrunner-1.9.2-dev python-gtkmozembed libswt-mozilla-gtk-3.5-jni couchdb-bin IIRC some time ago 0ad was able to link to the system spidermonkey.