Mozilla says the add-ons were advertised to users as being able bypass paywall restrictions on websites. They are incompatible, which means using both is NOT recommended as it may result in connectivity issues. However, the design of the Chrome API is completely different to this API. Google Chrome provides an extension API also called “proxy” which is functionally similar to this API, in that extensions can use it to implement a proxying policy. And where they want to intercept requests, they also need “host” permission for the URLs of intercepted requests.
Add-ons that use the proxy API need the “proxy” permission. The proxy API can be used by add-on developers as an event listener to intercept web requests, and return an object that describes whether and how to proxy them. The add-ons abused the proxy API to prevent users who had installed them from downloading updates, accessing updated blocklists, and updating remotely configured content.
The interference in itself was not the deciding factor, however.
In a Firefox security announcement, Mozilla said 455,000 users have downloaded Firefox add-ons that interfere with how they connect to the internet.
