Firefox 42 Stable, which will be released on November 3, 2015 if the schedule holds, will ship with Tracking Protection, a new feature enabled in Firefox's private browsing mode to improve a user's privacy while using the mode.
The feature blocks certain connections from being made to limit the exposure to tracking on the Internet. This works similar to how blocking extensions and programs
While privacy is certainly the main feature of Tracking Protection, a recent study has shown that it will reduce the load time of websites by 44% on average. The actual mileage varies for obvious reasons, as the feature won't help improve the load time if a site does not display advertisement or other tracking related scripts.
Side note: Nightly users have the option to enable the feature browser-wide so that it is not limited to the browser's private browsing mode only.
The initial version of Tracking Protection that will launch in Firefox 42 supports one list only that is either active or disabled.
This changes with the release of Firefox 43, scheduled to come out on December 5, 2015, as it will ship with blocklist selection options.
Instead of relying on a single list that you cannot change to protect you from Internet tracking, Firefox users can then select different lists based on personal preference and a desired level of protection.
Firefox 43 Tracking Protection Blocklist selection
Firefox 43 will ship with two lists by default that users can select between. The initial list that ships with Firefox 42 is enabled by default, and options to switch to another list are provided in the preferences.
- Load about:preferences#privacy in the Firefox address bar.
- Locate "Use Tracking Protection in Private Windows" and make sure it is checked.
- Click on the "Change Block List" button next to it to display all available blocklists.
- A prompt appears as an overlay displaying all lists and a selection option to switch between them.
Both lists that ship with Firefox 43 are powered by Disconnect.me.
- Basic Protection (recommended). Allows some trackers so websites function properly.
- Strict Protection. Blocks known trackers. Some sites may not function properly.
The Strict Protection policy blocks additional trackers that you may encounter on the Internet. The trade off is that you may run into sites that don't work properly because of the blocking.
Simply select the other list and click save changes to switch to it. You may switch back to the basic protection list at any time if websites fail to work properly after enabling the stricter list.
Firefox indicates blocked elements with a shield icon on the far left side of the browser's address bar. A click on it reveals additional information and an option to disable Tracking Protection for the session.
Options to display all servers and sites blocked by a tracking protection list, to bypass individual entries, to add new ones, or to add your own lists are not available currently. (via Sören Hentzschel)