Comment 8 for bug 1365408

The problem that compounds there is that the icon theme directory is not writable, so they can't be added the standard icon cache. We'd have to define a new icon cache that was built from the icons in click packages. Not impossible.

I think that probably a better solution for components that need to use icons in click packages to install click hooks that are appropriate for the icons they're interested in so they can build a cache of what they need. A generic cache here doesn't seem as useful when we can adequately detect changes on a per-component basis and evaluate fallbacks at package install time instead of runtime.