The recently launched Scribd subscription e-book service is adding an app for the Kindle Fire tablet as well as providing updates to its iOS and Android apps. The service, which provides users access to more than 100,000 titles for $8.99 a month, reports more than three million downloads of its app and rising usage by mobile device users.

In a phone interview, Scribd CEO and cofounder Trip Adler, said that more than 100,000 Kindle Fire users have visited the Scribd site asking for a compatible Scribd app. The new app can be downloaded here. The app does not support e-ink devices like the Kindle Paperwhite.

Along with the introduction of the Kindle Fire app, Scribd is also offering updates of its Apple and Android apps, and all apps will feature better fonts in more sizes, a ratings feature for content, a night reading mode and an upgrade to page tracking aligned to a book’s actual page number.

Adler also said that Scribd was used by more than 11 million mobile devices in December 2013. Mobile usage of the Scribd site, he said, was up five times over the same period in 2012 and “is growing 50% month-over-month.” He noted that the Scribd app is in the top 10 book apps in the Apple App Store and is the #1 book app in five countries around the world.

“The Kindle Fire app has been one of the most requested services since we launched,” Adler said, noting that he continues to talk to publishers to convince them to offer their titles via the service. But if the recent Digital Book World is any indication, skepticism among publishers over e-book subscription services in general remains. Adler acknowledged that publishers are cautious, but said, “We’ve seen some get on board quickly and others are taking their time but we continue to talk. This is new and publishers are hesitant but our numbers are growing and so is the revenue we’re paying to publishers.”

Adler emphasized again that the subscription mode is common in other media and that “it will spread to books, its inevitable.” He said user ratings of the Scribd service “are high,” and that “discoverability is our core pitch to publishers. Readers can read what they want and easily switch to other books, so we’re seeing a lot of reading behaviors. Some verticals attract different usage than others. We can spot reading patterns.”

He said that two-thirds of “our users are using the service to browse and read books they would not have read otherwise,” adding that “it’s our job to show that people want to read this way and to offer a meaningful distribution of revenue to the industry.”