a-a-s-p-d: add firefox on the package blacklist

And drop the path to plugins-container from the path blacklist because:
- the path belongs to firefox package
- the path is invalid, the correct path is:
  /usr/lib(64)/firefox/plugin-container

Resolves rhbz#1132018

Signed-off-by: Jakub Filak <jfilak@redhat.com>