Is it possible to reset all folder permissions?
Solution 1:
If you messed up a bunch of permissions in system directories, your best bet is to reinstall. Unless you can find somewhere a comprehensive list of the correct permissions, you probably won't get it right; furthermore, some things will fail, perhaps in surprising ways.
So, you're best off reinstalling in this situation. In the future, I'm sure you'll be more careful about what you chmod.