Malicious Firefox add-ons were misusing an API that controls how Firefox connects to the internet. Mozilla has blocked the malicious add-on in order to keep them from being installed by yet more users. Add-ons are powerful snippets of software that can be added to Firefox or other apps to customize the browser by doing things like preventing tracking, blocking ads, downloading videos from websites or providing content translation. Mozilla also made a change to how important requests such as update requests get handled by the browser.”]
Source: https://threatpost.com/mozilla-firefox-blocks-malicious-add-ons-installed-by-455k-users/175745/