XML parsing error on install (Gentoo amd64, binary Firefox package)

When I try to install the plugin on Firefox, I get the following error:

XML Parsing Error: not well-formed
Location: chrome://browser/content/preferences/permissions.xul
Line Number 1, Column 2:);
-^

I'm running 32-bit Firefox 2.0.0.13 (Gentoo's mozilla-firefox-bin package) on an x86_64 Linux 2.6.23 kernel.

Any suggestions?