There are literally hundreds online apps we enjoy using over time, but in reality we only use a handful of them regularly. For example I give some websites like Opinsy the option to connect to my Twitter and Facebook accounts. This is done by giving the app permission regarding the account. Users can usually review these permission given to apps and revoke them.
The problem for me is that I have to sign-in and check the settings for all the web services I use like Dropbox, Google, Facebook, Twitter and Windows Live ID for managing app permissions on all of them.
I found MyPermissions a very useful tool to clean up the apps I have given permission to connect. The site is actually not very complicated and does not require your ID at all. It simply links to the landing page of app permissions for the popular online websites which are used often to give permissions to apps.
MyPermissions also allows you to use your online profiles to give it permission to actively keep a watch on your app permission. It allows clean-up of permission with a single click and also alerts you to new permissions.
Unfortunately I could not find an add-on for Firefox. Try out MyPermissions and drop in your comments.