GetJar, the second largest mobile apps store, has seen their Facebook-shortcut app garner over 50M downloads in just six months. The online store, which caters to over 200 countries and supports 1700+ handsets, is apparently second only to Apple’s App Store on iTunes.

The GetJar app in question gives users a one-click MSS (Mobile Site Shortcut) link to Facebook’s mobile site on their handsets, so it’s not a full client like the iPhone app. While it may not seem like a big deal, given this is merely a shortcut icon to Facebook via a smartphone’s native Web browser, GetJar is still supposedly commanding roughly half of Facebook’s mobile market. An estimated 100M+ of Facebook’s 400M+ users access the site by mobile means, whether through an app or via a mobile version of the site.

In contrast, while Facebook’s usage from the iPhone jumped in Mar 2010, there are just under 32M active iPhone users of the official app, according to the official Fan Page. The Apple iPad does not yet have an official Facebook app, and the once-popular unofficial app was shut down. Thus GetJar’s Facebook shortcut app leads

Note: Developers looking to publish mobile apps on GetJar pay a per download fee of $0.01. Find out more on their developer page.