The workaround seems to be to make sure Firefox is started before viewing links from Facebook. We only recently saw this crash, so we suspect it was a Facebook app change that is the cause. However we are looking into ways to avoid this crash on the Firefox side. We may have a fix for this in our release for next Tuesday, in Firefox 37.

According to Facebook they have disable the function that was causing this crash for Firefox and Chrome for Android. You may need to update your Facebook app.