Thanks, JohnVV ... I hadn't noticed that "enabled" was set to 0. I fixed it, ran "yum install firefox-debug", and now have ...
> rpm -qv firefox-debuginfo
However, "firefox -g" still tells me I've got the wrong version debuginfo (3.0.4, instead of 3.0.6). Is there another repo that has the debuginfo for the current release of firefox?
Missing separate debuginfos, use: debuginfo-install firefox-3.0.6-1.fc10.i386