Mozilla and the Tor Project are in the early stages of exploring the inclusion of Tor's private browsing features within the Firefox web browser in the form of a privileged extension.

This comes on the heels of a previously expressed intention of including some Tor capabilities within Firefox in the form of a Super Private Browsing mode according to Mozilla's public Research Grants 2019H1 report from May.

Since that report was made public, the results of the Mozilla Research Grants for the first half of 2019 were published, with a research grant designed to look into the "Performance and Anonymity of HTTP/2 and HTTP/3 in Tor" being awarded to University of Illinois' Nikita Borisov.

The results stemming from the research will allow both the Tor Project and Mozilla to have a closer look at the potential performance issues the integration of Tor into the Firefox browser may cause.

These are some of the issues presented by a potential Tor integration within Firefox as part of the Super Private Browsing (SPB) mode, as stated by Mozilla in its Research Grants 2019H1 report:

What alternative protocol architectures and route selection protocols would offer acceptable gains in Tor performance? And would they preserve Tor properties? Is it truly possible to deploy Tor at scale? And what would the full integration of Tor and Firefox look like?

The Tor Project followed with their own call to the research community to send in applications for Mozilla Research Grants, mentioning that the most in need of attention is Tor's network performance which also represents "one of the largest barriers to its adoption."

'Super Private Browsing' mode becomes a privileged add-on

However, about a week ago, during a Tor meeting of the core Tor team, developers, volunteers, as well as invited guests that took place in Stockholm, the plans to create a Firefox Super Private Browsing mode got slightly changed, with the new proposal being to create a "Tor mode" extension for Firefox.

Due to the complexity of integrating Tor directly into Firefox, Mozilla and the Tor team are exploring the use of a privileged extension to gauge the performance impact before embedding within the browser's codebase.

The Tor mode add-on proposal is described like this in the meeting notes:

There is an idea to, in the future, have Firefox use Tor in private browsing mode, or an a new extra-private mode. That will take a lot of engineering work and buy-in. To help smooth the path, there is a proposal for a "Tor mode" addon. This would not be packaged with the browser by default, but would be something that users could download from addons.mozilla.org to give them a "Tor mode" button or similar. It would allow users to experience what an eventual full integration with Tor could look like. It could also help gauge interest by counting downloads, etc. [emphasis added]

Additionally, the Tor mode extension is described as a "privileged add-on [..] with elevated privileges compared to a standard WebExtension."

"The addon would configure the browser to use tor as a proxy, as well as setting various prefs to prevent proxy bypasses and resist fingerprinting, much like those set by Tor Browser."

"Discussion of visual options for UI. Clicking the Tor-mode button would probably open a new window that uses a dedicated profile. This is because some of the prefs that the addon has to set are global to a profile, not to a window or a tab."

Furthermore, since passing unauthenticated HTTP traffic through tor exit nodes could be dangerous and including NoScript does not improve the user experience, the "easiest solution is to enforce (require) HTTPS when in Tor mode."

Tor Browser patch uplifting on hold

The Tor Project told BleepingComputer that they "are in the early stages of exploring this with Mozilla. Tor has never been deployed at this scale, so the Tor Project and Mozilla are both researching considerations to see if integration is possible."

Also, Firefox Browser Engineering Senior Director Selena Deckelmann told BleepingComputer that "the discussions during the Tor gathering did include a Mozilla representative. We haven’t yet made a decision to create a Tor mode."

"We continue to explore how we can best support the Tor engineering team’s use of Firefox through the Tor Uplift project, as well as possible future integrations that would enhance the experience of our users."

Examples of active Tor Uplift project bugs

While Mozilla's developers have already started working on including some Tor features into Firefox as part of the Tor Uplift project designed to "land all Tor Browser patches so that Tor can directly use Firefox main trunk instead of a fork", patch uplifting will be paused for at least a few months according to the Tor meeting notes.

A color-coded list of patches from Tor Browser tickets considered for uplifting into the Firefox codebase is currently available HERE.

Tor Browser features included in Firefox

Mozilla has already integrated several Tor Browser privacy features into Firefox over the years after detecting attempts to fingerprint their users.

For example, in December 2016, Mozilla engineers included a new mechanism with the release of Firefox 52 which automatically blocks websites from fingerprinting users with the help of system fonts.

Also, Mozilla borrowed yet another Tor Browser feature allowing Firefox to prevent user fingerprinting attempts via the HTML5 canvas element during October 2017.

Brave Private Window

Mozilla is not the first to consider using Tor to boost the Firefox users' privacy, with Brave already having included the open-source online anonymity Tor software within its private browsing mode.

This allows Brave users to hide their browsing habits from employers and Internet Service Providers, as well as conceal their IP addresses from the websites they visit.

Brave's newly acquired Tor capabilities allow its users to prevent tracking while browsing the web and protecting their privacy without having to install any additional software on their computers.

As The Tor Project also told BleepingComputer, "Integrating Tor into Firefox would bring real private browsing and a safer internet experience to an unprecedented number of people around the world, so we are very excited to be exploring this possibility."