zac4firefox is a Firefox extension that enables client-side enforcement of ZAC policies. The idea is to be able to restrict the actions that the scripts of pages visited by the user can perform.

The extension can be downloaded from here. The extension is compatible with Firefox 3.6.

• Due to the performance penalties introduced by the transformation phase required by AspectScript, the observable overhead ranges from acceptable to very high, depending on the load of JavaScript computation of the visited page.
• Due to the limitations introduced by the parser used by AspectScript (the JavaScript parser from the Narcissus project), some scripts are not transformed, and therefore are not subject to ZAC policies. When this occur, the following notification is presented to the user:

• Once pages and scripts are transformed, ZAC caches them to improve the performance the next time the page is visited. This cache is erased when the browser is started and when the active policies change.