For some years now Firefox has had the rather convenient privacy feature of not showing your NSFW bookmark links in its New Tab Page, which is normally a convenient location to return to your most frequently viewed sites.

While this would not stop anyone from viewing your browser history, it would prevent some embarrassment from people who are shoulder surfing.

The feature is based on a list of around 2900 sites which can be seen on Github here (as uncovered by this Reddit thread.) Firefox compares a hash of your bookmarks against a local list of hashes from the site addresses, and if they match they do not qualify for being proudly displayed on your New Tab page.

While we can see the benefits of this feature, it turns out the origin is rather less wholesome.

While Mozilla has been in the news lately for various attempts to monetize their browser, they have been at this for a long time, and this feature dates back 4 years when Mozilla was experimenting with replacing some of the New Tab site tiles with Sponsered Links.

See the Trulia tile above for an example.

The issue, as aptly described on Bugzilla was:

Commercial partners do not want their content to be negatively associated with adult content. In the context of Suggested Tiles, this means no sponsored or affiliate tiles should appear within same browser viewport. As an example, MGM would not want a 007 DVD release to be appearing within the same page…

That Sponsored Tile project never shipped in the end, but it turns out the NSFW filter remains active.

Does all this behind the scenes ad-based activity make our readers think differently about the non-profit Mozilla foundation? Let us know below.

Via Techdows.com