In World War 2 the Allies didn't win because they had the best tanks and airplanes. They won because they - the US, really - could build them much faster than Axis. It's a numbers game.

Edit: One could argue this isn't what the news article is about but what's losing 50M in a market of billions? A device, specially a smartphone, is a delivery mechanism for services and in this day and age when internet access (apps) has become massified, having "choice" is irrelevant as far as browser marketshare goes. I do hope Firefox continues because I quite enjoy using it but if they do fold someday I won't be surprised.