The newest version of Mozilla's Firefox browser, version 42, comes with a privacy feature that lets users block automatic trackers with a privacy mode. Private Browsing is based on Disconnect, an anti-tracking service that used to be bundled as an add-on in Firefox.
There's one additional new feature worth noting: a symbol in the tabs that shows when a site to be opened is going to come up playing music or other annoying audio content. Users can mute those sites before they start with a single click.
Additionally, Firefox is now available in a version for 64-bit operating systems.