Today, Mozilla announced that it will be running an experiment where a small group of Firefox users will be shown an ad to purchase a subscription to ProtonVPN, as spotted by ZDNet. In a blog post, Mozilla says it picked ProtonVPN for the partnership due to factors like transparency and data retention policies.

Beginning on October 24th, the ad will be shown to select US-based Firefox users who are running the latest version — Firefox 62 — on desktop. If eligible and browsing on an unsecured network, you’ll be shown an ad in the top-right corner of your Firefox window that prompts you to click through to a signup page.

Mozilla is offering ProtonVPN’s services for $10 a month, which is the same as buying the package directly through ProtonVPN (though ProtonVPN also offers a yearly plan that knocks the price down to $8 a month). But, the majority of the revenue from ProtonVPN subscriptions that are processed through Mozilla will go directly to Mozilla. Both companies are banking that people will have good will about paying a little more in order to support their “shared goal of making the internet a safer place.”

The partnership is useful, and it does make sense, but ultimately, it is an advertisement for a subscription service that will be built into a browser. It’s also not Mozilla’s first foray with baking monetized content into Firefox. New tabs show recommended articles from Pocket, and sometimes those articles are sponsored. If the program proves successful, ProtonVPN says it could expand to all of Mozilla’s more than 300 million users.