Mozilla engineers are planning to notify users with a popup every time the page wants to retrieve data from HTML, similar to asking the right to use webcam and microphone.
Firefox 58 plans to release on January 16, 2018.
This is the second feature Mozilla borrowed from the Tor Project. Previously, Firefox 52 had a mechanism for not allowing websites to track users through system fonts.
The effort to make Firefox more solid is part of the Tor Uplift project, which initiatives to bring Tor Browser privacy features to Firefox. Tor is built on Firefox ESR and often takes features from Firefox.
In August 2016, Mozilla blocked a list of trace script host URLs. Earlier, Firefox also removed Battery Status API to improve user privacy.