How to Enable Letterboxing Feature in Mozilla Firefox 67

Firefox Nighly logo
Firefox 67, slated for May, will come with an anti-fingerprinting feature called Letterboxing to tackle online ads. A beta version is available now.

Mozilla Firefox is now bringing in a new anti-fingerprinting feature to which it has assigned the name “Letterboxing.”

The feature will be made universally available for all Firefox users in the next version of the browser, Firefox 67, which is to be released this May.

However, a trial or beta version is available in case you are interested in testing the feature out.

Window Resizing Technique Used

Firefox has gone with the theory that the window size opened by the user in the browser plays a key role in the way the advertisers engage in fingerprinting, and the “Letterboxing” feature is built on this technique of denying the entity engaged in the fingerprinting activity to get the size of the window.

This is done through dividing the window in multiple boxes of content in a certain ratio of pixels like 200×100 pixels. This generates a certain gap in the margins so that the window size cannot be determined.

The addition of gray space on all sides is the basic technique being employed here. And the objective of misleading the code used by the advertiser to do fingerprinting is successfully accomplished.

Earlier Used in the Tor Browser

As you may be aware, the Tor browser that is mostly used in the darknet environment is built on the Firefox platform with the codes drawn from it. The Letterboxing technique was first introduced in the Tor browser in 2015.

Mozilla’s adoption of the feature for Firefox is expected to go smoothly.

Enabling Letterboxing in Your Firefox Browser

You may not have to wait until May to know and use this anti-fingerprinting feature. But you will need to download the latest version of Firefox Nightly for this.

Here are the steps:

  1. Download and install the latest Firefox Nightly version.

Firefox Nighly

2. Launch the browser.

3. Next, you should type about:config in the browser bar.

about - config

4. The bar on top has a search icon. There, type or copy/paste the following code: resistFingerprinting


5. There are several entries here on this window and against each, in the adjacent column, there will be the status True or False.

6. When you type the above resistFingerprinting it will appear with the default False against it. (That’s how it is programmed—Letterboxing or anti-fingerprinting is not enabled by default. You will have to manually enable it each time.)

7. Further to the right you will find the Toggle button.

8. Click on it to change to status to True.


9. This enables the anti-fingerprinting function in the browser to be turned on.

The above steps will help you enable Letterboxing in your Mozilla Firefox browser.

Check If the Feature Has Been Enabled

There are ways to make sure the anti-fingerprinting feature you just enabled is indeed working fine or not. Browserleaks is a website that can help you determine how the anti-fingerprinting feature remains on. Since you have enabled this feature in the Firefox Nightly browser, you need to be on that browser while accessing the Browserleaks site.

Once there, you can check the viewport and screen resolution. You can take some time and first check these parameters with the Letterboxing enabled. Then go back through the same route as above and toggle it to False, thereby disabling the feature.

When you go to the Browserleaks site with the feature disabled, you will find the window sizes not altering, confirming that you did enable it correctly in the first place.

Some Inconveniences with the Feature Enabled

While this sounds quite exciting and appears a useful tool to have and to block advertisers in your computer, experts warn that with the anti-fingerprinting feature turned on, there are a few operations which can get affected too.

One of them is the captchas that many sites ask you to type as a part of the verification process. As per reports, the captcha verification may fail with the feature enabled.

Either you have the patience to go through the motions of enabling and disabling the feature, or you can enable it only when you find it absolutely necessary.

Will Mozilla Stick with May 2019 Release Date?

Another question being posed is whether the scheduled release of the Firefox 67 browser version with the Letterboxing feature will happen on time or not. The question on some people’s minds is if the feature should be set in the True position instead of False, making it the default option.

Based on this and other factors, people familiar with the way Mozilla works are wondering if Firefox 67 will keep its release date on May 14 as indicated.

Data Security Is Paramount

All these efforts are part of the objective to protect the personal information that users have on their computers. There are several ways to do this. Antivirus programs are considered one way to block hackers from stealing users’ data. But the way to handle advertisers effectively was still eluding technology developers. The anti-fingerprinting feature being introduced by Mozilla Firefox in the form of Letterboxing might be the answer.

You have to wait until mid-May or even June to know if this new technique is effective in slowing down or stopping the unwanted advertising you may be faced with.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.